U.S. patent number 6,941,098 [Application Number 10/385,535] was granted by the patent office on 2005-09-06 for classifier, developer, and image forming apparatus.
This patent grant is currently assigned to Ricoh Company, LTD. Invention is credited to Yutaka Ebi, Toshiroh Higuchi, Masanori Horike, Yohichiro Miyaguchi, Takeshi Takemoto.
United States Patent |
6,941,098 |
Miyaguchi , et al. |
September 6, 2005 |
Classifier, developer, and image forming apparatus
Abstract
A classifier having a simple constitution for classifying powder
with a high accuracy is provided. The classifier is provided with a
transfer board having a plurality of electrodes for generating
electric fields for transferring and hopping the powder by an
electrostatic force. The classifier is further provided with an
opposite roller generating an electric field for transporting and
attaching the powder (toner) transferred and hopped on the transfer
board to the opposite roller, which is opposite to the transfer
board.
Inventors: |
Miyaguchi; Yohichiro
(Kanagawa-ken, JP), Horike; Masanori (Kanagawa-ken,
JP), Takemoto; Takeshi (Kanagawa-ken, JP),
Ebi; Yutaka (Kanagawa-ken, JP), Higuchi; Toshiroh
(Kanagawa-ken, JP) |
Assignee: |
Ricoh Company, LTD (Tokyo,
JP)
|
Family
ID: |
29200048 |
Appl.
No.: |
10/385,535 |
Filed: |
March 12, 2003 |
Foreign Application Priority Data
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Mar 13, 2002 [JP] |
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2002-069106 |
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Current U.S.
Class: |
399/252; 399/266;
399/291 |
Current CPC
Class: |
G03G
15/08 (20130101); G03G 2215/0619 (20130101) |
Current International
Class: |
G03G
15/08 (20060101); G03G 015/08 () |
Field of
Search: |
;399/251,265,266,289,290,291,252,294,295 ;347/55,140 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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63-013068 |
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Jan 1988 |
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JP |
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07-267363 |
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Oct 1995 |
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JP |
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08-149859 |
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Jun 1996 |
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JP |
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2000-143026 |
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May 2000 |
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JP |
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2002-287495 |
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Oct 2002 |
|
JP |
|
Other References
US. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
.
U.S. Appl. No. 10/863,294, filed Jun. 9, 2004, Horike et al. .
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
.
U.S. Appl. No. 10/805,362, filed Mar. 22, 2004, Miyaguchi et al.
.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
.
U.S. Appl. No. 10/817,249, filed Apr. 5, 2004, Nakano et al. .
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
.
U.S. Appl. No. 10/659,468, filed Sep. 11, 2003, Shakuto et al.
.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et al.
.
U.S. Appl. No. 10/825,318, Apr. 16, 2004, Naruse et al. .
U.S. Appl. No. 09/330,669, filed Jun. 11, 1999, Yasui. .
U.S. Appl. No. 09/765,608, filed Jan. 22, 2001, Hayashi et al.
.
U.S. Appl. No. 09/948,576, filed Sep. 10, 2001, Miyaguchi et al.
.
U.S. Appl. No. 10/050,865, filed Jan. 18, 2002, Ohtaka et al. .
U.S. Appl. No. 10/098,125, filed Mar. 15, 2002, Miyaguchi et al.
.
U.S. Appl. No. 10/385,535, filed Mar. 12, 2003, Miyaguchi et
al..
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Primary Examiner: Tran; Hoan
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said opposite member is an opposite
transfer member which has a plurality of electrodes for generating
electric fields and which is configured to for transfer said powder
by an electrostatic force.
2. The classifier of claim 1, wherein part or the whole of said
opposite transfer member is inclined position against said transfer
member.
3. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said opposite member is a rotary
roller member.
4. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said opposite member is a rotary
pelt member.
5. The classifier of claim 4, wherein said belt member is inclined
against said transfer member.
6. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said opposite member comprises
electrode wires.
7. The classifier of claim 6, wherein said each of the electrode
wires is covered with a protective layer.
8. The classifier of claim 6, further comprising a slit member
having slit holes arranged between the electrode wires, which are
arranged at a position substantially opposite to said transfer
member, and the transfer member.
9. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said opposite member comprises an
array of electrode wires.
10. The classifier of claim 9, wherein a voltage for generating
electric fields is applied to each of the electrode wires.
11. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said opposite member comprises a
slit member having slit holes; and electrodes formed on wall
surfaces of the slit holes.
12. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein a width of each of said electrodes
of said transfer member in a transporting direction of said powder
is 1 to 20 times an average grain diameter of said powder, and each
space between said electrodes in the transporting direction of said
powder is 1 to 20 times the average grain diameter of said powder,
wherein drive waveforms of n phases are applied to each of the
plurality of electrodes, wherein a represents an integer not less
than 3.
13. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein said transfer member has an
inorganic or organic surface protective layer covering said
plurality of electrodes, and wherein a thickness of the surface
protective layer is not more than 10 .mu.m.
14. A classifier for classifying a powder comprising: a transfer
member which has a plurality of electrodes for generating electric
fields and which is configured to transport said powder while
transferring and hopping said powder by an electrostatic force; and
an opposite member configured to selectively catch particles of
said powder transferred and hopped by the transfer member, the
opposite member being arranged in a position substantially opposite
to the transfer member, wherein the classifier bas a plurality of
said opposite members, and the plurality of said opposite members
selectively catch the particles of said powder depending on a
quantity of charge or a mass of the particles of said powder.
15. A developer, comprising: a classifier configured to classify a
powder; and a developing means for developing a latent image on a
latent image carrier the classified powder to form a visual image
on the latent image carrier, and wherein said classifier comprises:
a transfer member which has a plurality of electrodes for
generating electric fields and which is configured to transport
said powder while transferring and hopping said powder by an
electrostatic force; and an opposite member configured to
selectively catch particles of said powder transferred and hopped
by the transfer member, the opposite member being arranged in a
position substantially opposite to the transfer member.
16. The developer of claim 15, wherein said developing means
comprises a developing roller facing to said latent image
carrier.
17. The developer of claim 16, wherein said developing roller also
functions as said opposite member.
18. The developer of claim 15, wherein said developing means is a
member having a plurality of electrodes for generating electric
fields for transferring and hopping the powder by an electrostatic
force at a position near said latent image carrier.
19. The developer of claim 18, wherein said member having a
plurality of electrodes also functions as said opposite member.
20. The developer of claim 15, wherein said developer means
comprises a rotary belt facing to said latent image carrier.
21. The developer of claim 20, wherein said rotary belt member also
functions as said opposite member.
22. An image forming apparatus, comprising: a latent image carrier;
and a developer configured to develop a latent image with a powder,
wherein the developer is the developer of claim 15.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese
application serial no.2002-069106, filed on Mar. 13, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a classifier, a developer, and
an image forming apparatus.
2. Description of Related Art
Copiers, printers, facsimiles and the like, have been known as
image forming apparatuses. Some of them employs such an image
forming process that a latent image is formed on a latent image
carrier using an electrophotographic process, and a powder
developing agent (hereinafter, also called toner) is attached to
the latent image to develop it as a visible toner image, then the
toner image is transferred to a recording medium, including an
intermediate transferring member, so that an image is formed.
As a developer developing latent images, which is employed for such
image forming apparatuses, such a developer has been known that
toner agitated in a developer is carried on the surface of a
developing roller, which is a developing agent carrier, and the
developing roller is rotated to transfer the toner to the position
where the toner is opposite to the surface of a latent image
carrier, then the latent image of latent image carrier is
developed. After the development, the part of the toner that has
not been transferred to the latent image carrier is collected into
the developer as the developing roller is rotated, then new toner
is agitated, charged and carried on the developing roller to be
transferred again.
Another application of an image forming apparatus is also disclosed
in the Japanese Laid Open Publication No. 9-197781 and 9-329947. In
the disclosed apparatus, a jumping developing method is employed,
in which toner is transferred from a developing roller to a latent
image carrier without any contact in-between.
Another application of an image forming apparatus is further
disclosed in the Japanese Laid Open Publication No. 5-19615. In
this apparatus, toner is transferred on the surface of a developing
roller by an electrostatic force, and an attractive force generated
between the toner and a latent image carrier separates the toner
from the surface of the developing roller, thus attaching the toner
to the surface of the latent image carrier. Still, another
application of an image forming apparatus is disclosed in the
Japanese Laid Open Publication No. 59-181375. In this application,
toner is transferred to a position where the toner is opposite to a
latent image carrier, using a transfer board for transferring the
toner by an electrostatic force, then the toner is separated by an
attractive force generated between the toner and the latent image
carrier and is attached on the surface of latent image carrier.
The Japanese Laid Open Publication No. 7-267363 discloses a powder
transfer apparatus for transferring powder, such as toner, using
space-traveling-waves fields. This apparatus is provided with
electrodes, to which a drive voltage is applied to form space
traveling wave fields around the electrodes. The traveling wave
fields repel and drive the charged powder, transferring it in the
transporting direction of electric fields.
As for a classifier for classifying powder, such as toner, a
classifier using a screening or wind force classifying method is
known. Other application is disclosed in the Japanese Laid Open
Publication No. 8-149859, in which such a classifier is described
that classification (separation) is carried out by using the
space-traveling-wave fields described above, which make
electrostatic force, gravity, and centrifugal force act all
together on toner. Besides, the Japanese Laid Open Publication No.
2000-140683 and the Japanese Laid Open Publication No. 2000-140700
disclosed another method such that a voltage is applied to generate
a potential vertical to the transfer direction of charged powder so
that the powder is separated from the transfer surface according to
its specific charge.
To form high quality images using such image forming apparatuses,
it is important to keep uniform the quantity of charge and mass of
the grains of toner for development. However, it has been found
difficult for conventional image forming apparatuses to achieve a
uniform attachment of toner. Therefore, in conventional methods,
toner is pre-classified in the manufacturing process by screening
or applying wind force to uniform the toner to a certain extent,
and is supplied to an image forming apparatus.
However, even if the substantially uniformed toner is supplied to
the image forming apparatus, the toner is not always uniformly
charged because the toner is charged in the image forming apparatus
in the first place. Charging the toner in the apparatus inevitably
cause the unevenness of q/m (quantity of charge per mass) and of
the diameters of the grains of toner, thus posing a problem that
there is a limit for forming a high quality image.
Besides, a conventional classifier tends to become a large-sized
one. A classifier using a method of electrostatic transfer and
gravity to classify toner also has a problem that an exact
classification is difficult.
SUMMARY OF THE INVENTION
According to the foregoing description, it is an object of this
invention to provide a classifier having a simple constitution,
which achieves a high classification accuracy utilizing a ETH
(Electrostatic Transport & Hopping) phenomenon, a developer
provided with the classifier, which enables high quality
development, and an image forming apparatus provided with the above
classifier and developer enabling the forming of high quality
images.
The ETH represents a phenomenon that powder receives the energy of
phase-shifting fields and the energy is transformed into a
mechanical energy, which moves the powder itself dynamically. The
phenomenon includes the horizontal moves (transfer) and vertical
moves (hopping) of the powder by an electrostatic force. It is the
phenomenon that the powder comes to have a component in the
transporting direction and hops on the surface of an electrostatic
transfer member, due to the phase-shifting fields. Hereinafter, a
development utilizing the ETH phenomenon is called ETH
development.
In separately describing the behavior of powder on a transfer
member, hereinafter, the terms of "transfer", "transfer velocity",
"transfer direction" and "transfer distance" are used for the
powder moving in the horizontal direction to a board, the terms of
"hopping", "hopping velocity", "hopping direction" and "hopping
height (distance)" are used for the powder jumping up (moving) in
the vertical direction on the board, and "transfer and hopping" on
the transfer member is generally called "transport." The term
"transfer" included in the terms "transfer apparatus" and "transfer
board" is synonymous with "transport."
The present invention provides a classifier for classifying a
powder. The classifier comprises a transfer member which has a
plurality of electrodes for generating electric fields and which is
configured to transport said powder while transferring and hopping
said powder by an electrostatic force; and an opposite member
configured to selectively catch particles of said powder
transferred and hopped by the transfer member, the opposite member
being arranged in a position substantially opposite to the transfer
member. It will be appreciated that, in this specification, the
term "powder" is used to also represent "fine powder", "grains of
powder", "fine grains of powder", "particles", "fine particles",
etc, so such terms are not excluded as the terminology not standing
for the definition of "powder."
The opposite member may be an opposite transfer member which has a
plurality of electrodes for generating electric fields and which is
configured to for transfer said powder by an electrostatic force.
In this case, the opposite transfer member may be arranged in such
a way that part or the whole of the opposite transfer member is
inclined against the transfer member.
The opposite member may be provided as a rotary roller member, or a
rotary belt member which may be inclined against the transfer
member.
Further, the opposite member may comprise an array of electrode
wires, where a voltage for generating electric fields is applied to
each of the electrode wires. It is desirable to form a protective
film on the electrode wires. It is also desirable to further
comprise a slit member having slit holes arranged between the
electrode wires, which are arranged at a position substantially
opposite to said transfer member, and the transfer member.
Further, the opposite member may comprise a slit member having slit
holes; and electrodes formed on wall surfaces of the slit
holes.
It is desirable for the transfer member of the classifiers
described above that the width of respective electrodes of the
transfer member in the transporting direction of the powder be more
than 1 to 20 times the average grain diameter of the powder, as
well as the space between respective electrodes in the same
direction be also more than 1 to 20 times the average grain
diameter of the powder, and that drive waveforms of more than n (a
natural number of 3 or more) phases be applied to each
electrode.
It is also desirable that the transfer member has an organic or
inorganic surface protective layer whose thickness is not more than
10 .mu.m.
It may be also arranged in such a way that the classifier has a
plurality of said opposite members, and the plurality of said
opposite members selectively catch the particles of said powder
depending on a quantity of charge or a mass of the particles of
said powder.
The present invention further provides a classifier for classifying
powder, in which the classifier transports said powder while
transferring and hopping the powder by an electrostatic force,
comprising a member configured to selectively catch particles of
said powder transferred and hopped by forming an electric
field.
The invention also provides a developer, comprising: a classifier
configured to classify a powder; and a developing means for
developing a latent image on a latent image carrier the classified
powder to form a visual image on the latent image carrier. The
classifier is any classifier described above.
The developing means may comprise a developing roller facing to the
latent image carrier, which can also be used as the opposite
member. The developing means may also be a member having a
plurality of electrodes for generating electric fields for
transferring and hopping the powder by an electrostatic force at a
position near the latent image carrier, and the member can also be
used as the opposite member. Further, the developing means may
comprises a rotary belt member, at least part of which is opposite
to the latent image carrier, and the belt member can also be used
as the opposite member.
The present invention further provides an image forming apparatus,
comprising: a latent image carrier; and a developer configured to
develop a latent image with a powder. The developer can be the
developer mentioned above.
BRIEF DESCRIPTION OF THE DRAWINGS
While the specification concludes with claims particularly pointing
out and distinctly claiming the subject matter which is regarded as
the invention, the objects and features of the invention and
further objects, features and advantages thereof will be better
understood from the flowing description taken in connection with
the accompanying drawings in which:
FIG. 1 is a schematic block diagram for explaining the first
embodiment of the classifier of this invention;
FIG. 2 is a front view of the transfer board of the classifier of
this invention;
FIG. 3 is a flat view of the above transfer board;
FIG. 4 is an explanatory drawing showing one example of drive
waveforms which are given to the transfer board;
FIG. 5 is an explanatory drawing for describing the transfer and
hopping of powder;
FIG. 6 is an explanatory drawing showing a specific example of the
transfer and hopping of the powder;
FIG. 7 is an explanatory drawing for describing the time and duty
of applied voltage generating drive waveforms;
FIG. 8 is an explanatory drawing showing one example of the drive
waveforms, which is generated by an applied voltage with a duty of
67%;
FIG. 9 is an explanatory drawing showing one example of the drive
waveforms, which is generated by an applied voltage with a duty of
33%;
FIG. 10 is an explanatory drawing for describing the width of and
the spaces between electrodes;
FIG. 11 is an explanatory drawing for describing the relation
between the width of electrodes and the electric field (X
direction) at the end of an electrode with zero voltage;
FIG. 12 is an explanatory drawing for describing the relation
between the width of electrodes and the electric field (Y
direction) at the end of an electrode with zero voltage;
FIG. 13 is an explanatory drawing for describing the shape of drive
waveform;
FIG. 14 is an explanatory drawing for describing the relation
between the shape of drive waveform and the distance of horizontal
travel of the powder;
FIG. 15 is an explanatory drawing for describing the relation
between the voltage value of drive waveform and the Y directional
velocity and hopping height of the powder;
FIG. 16 is an explanatory drawing for describing one example of the
relation between a thick film of surface protective layer and the
strength of fields;
FIG. 17 is an explanatory drawing for describing the relation
between the thick film of surface protective layer and the strength
of fields;
FIG. 18 is another explanatory drawing for describing the relation
between the thick film of surface protective layer and the strength
of fields;
FIG. 19 is an explanatory drawing for describing the operation of
the classifier of the first embodiment;
FIG. 20 is an explanatory drawing for describing the classifying
operation of the above classifier;
FIG. 21 is an explanatory drawing for describing one example
showing that the grains of toner is classified according to the
quantity of charge by a roller applied voltage.
FIG. 22 is an explanatory drawing for further describing the
example shown in FIG. 21;
FIG. 23 is a schematic block diagram for explaining the second
embodiment of the classifier of this invention;
FIG. 24 is a schematic block diagram for explaining the third
embodiment of the classifier of this invention;
FIG. 25 is a schematic block diagram for explaining the fourth
embodiment of the classifier of this invention;
FIG. 26 is a schematic block diagram for explaining the fifth
embodiment of the classifier of this invention;
FIG. 27 is a schematic block diagram for explaining the sixth
embodiment of the classifier of this invention;
FIG. 28 is a schematic block diagram for explaining the seventh
embodiment of the classifier of this invention;
FIG. 29 is a schematic block diagram for explaining the eighth
embodiment of the classifier of this invention;
FIG. 30 is a schematic block diagram for explaining the ninth
embodiment of the classifier of this invention;
FIG. 31 is an explanatory drawing for describing the different
shapes of the slit holes and electrodes employed in the ninth
embodiment of the classifier;
FIG. 32 is a schematic block diagram for explaining the tenth
embodiment of the classifier of this invention;
FIG. 33 is an explanatory drawing for describing the constitution
of the electrode wires in the tenth embodiment and another example
of the same;
FIG. 34 is a schematic block diagram for explaining the eleventh
embodiment of the classifier of this invention;
FIG. 35 is an explanatory drawing showing different examples of the
drive waveforms generated through the bias drive circuits in the
eleventh embodiment;
FIG. 36 is an important element on large scale for explaining the
twelfth embodiment of the classifier of this invention;
FIG. 37 is a schematic block diagram for explaining the thirteenth
embodiment of the classifier of this invention;
FIG. 38 is an enlarged detail of FIG. 37;
FIG. 39 is a schematic block diagram for explaining the fourteenth
embodiment of the classifier of this invention;
FIG. 40 is a plain view showing the electrode wire line member in
the fourteenth embodiment;
FIG. 41 is a schematic block diagram for explaining the fifteenth
embodiment of the classifier of this invention;
FIG. 42 is a schematic block diagram for explaining the first
embodiment of the developer of this invention;
FIG. 43 is a schematic block diagram for explaining the second
embodiment of the developer of this invention;
FIG. 44 is a schematic block diagram for explaining the third
embodiment of the developer of this invention;
FIG. 45 is a schematic block diagram for explaining the fourth
embodiment of the developer of this invention;
FIG. 46 is a schematic block diagram for explaining the fifth
embodiment of the developer of this invention;
FIG. 47 is a schematic block diagram for explaining the first
embodiment of the image forming apparatus of this invention;
FIG. 48 is a schematic block diagram for explaining the second
embodiment of the image forming apparatus of this invention;
FIG. 49 is a magnified view showing the developer of the above
image forming apparatus;
FIG. 50 is an explanatory drawing for describing the developing
operation of the above developer;
FIG. 51 is an explanatory drawing for describing one example of the
relation between the drive frequency of drive waveform and a toner
transfer velocity;
FIG. 52 is an explanatory drawing for describing other examples of
the drive waveforms;
FIG. 53 is a flat view showing a powder charging and selecting
apparatus constituted according to the classifier of this
invention; and
FIG. 54 is another flat view showing the powder charging and
selecting apparatus constituted according to the classifier of this
invention;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, the preferred embodiments of the present invention are
to be described referring to the drawings. First, the first
embodiment of the classifier of this invention is described
referring to FIG. 1, which is a schematic block diagram of the
classifier.
The classifier comprises a transfer board 1, which is a transfer
member having a plurality of electrodes for generating electric
fields for transferring and hopping toner, i.e., powder, and an
opposite roller 2, which is an opposite member (also functions as
other member) to which the toner transferred on the transfer board
1 is transported and attached.
The classifier also comprises a drive circuit 3 applying drive
waveforms Pv1 having n phases (n stands for a natural number of 3
or more) to each electrode of the transfer board 1 so as to
generate traveling waveform fields for transferring and hopping the
toner. The opposite roller 2 is provided with a bias power source 4
for applying a bias voltage having a polarity opposite to the
charge of the toner. The bias voltage is positive when the toner is
negatively charged, and the bias voltage is negative when the toner
is positively charged. It will be appreciated that the description
is made on the assumption that the toner is negatively charged.
A charging means 5 is arranged on the toner supply side of the
transfer board 1. The charging means 5 comprises a charging brush
(or maybe a unit other than the charging brush) and a magnet roller
for charging the toner, which is supplied from a toner supply (not
shown in the drawings) or recovered, and sending the toner to the
transfer board 1. A collecting electrode 6 is arranged on the
residual toner discharging side of the transfer board 1, where the
electrode 6 collects the part of toner that is not transported and
attached to the opposite roller 2. A recovery/transport member 7 is
also provided for transporting the toner collected by the
collecting electrode 6 to the charging means 5 by an electrostatic
force, where the recovery/transport member is provided with a drive
circuit 8 for applying a drive voltage Pv2 to the electrodes
provided on the recovery/transport member 7, the drive voltage
generating electric fields for transporting the toner.
The opposite member 2 has a blade 9 for removing the toner sticking
on the opposite roller 2, and a gutter 10 for storing the toner
removed by the blade 9. (The removed toner can be supplied to the
developing means of the developer).
Now, the transfer board 1 is described in detail referring to FIG.
2 and FIG. 3. FIG. 2 is the schematic sectional view of the
transfer board 1 and FIG. 3 is the flat view of the same. The
transfer board 1 has a support board 11 on which a plurality of
electrodes 12 are arranged at every a prescribed distance in the
transport direction of powder, (i.e., transporting direction of
powder or moving direction of powder shown by an arrow in FIG. 2),
where three units of the electrode 12 are made one set for
generating drive waveforms. The support board 11 is laminated with
a surface protective film 13 made of an inorganic or organic
insulating material, which functions as an insulating transfer
surface forming member, i.e., a protective film covering the
surface of the electrodes 12, on which a transfer surface is
formed.
The support board 11 may be a board consisting of such an
insulating material as glass, resin, or ceramic, or a board
consisting of a conductive material, such as SUS, with an
insulating film, such as SiO.sub.2, formed thereon, or a board
consisting of a deformable material, such as polyimide.
In forming the electrodes 12, a film of conductive material, such
as Al, Ni--CR and the like, is formed on the support board 11 at a
thickness of 0.1 to 1.0 .mu.m, or desirably a thickness of 0.5 to
2.0 .mu.m. Then a required electrode patterns is formed on the
film, using a photolithography technique, to form the electrodes
12. The width L of the respective electrodes 12 in the transporting
direction of powder is made 1 to 20 times the average diameter of
the grains of traveling powder. The space R between each electrode
12 in the transporting direction of powder is also made 1 to 20
times the average diameter of the grains of traveling powder.
The surface protective layer 13 is formed as a film consisting of
such a substance as SiO.sub.2, TiO.sub.2, TiO.sub.4, SiON, BN, TiN,
or Ta.sub.2 O.sub.5, where the thickness of the film is 0.5 to 10
.mu.m, or desirably 0.5 to 3 .mu.m.
The recovery/transport member 7 has the same constitution as that
of the transfer board 1. The base board of the recovery/transport
member 7 is a flexible board consisting of a polyimide film or the
like on which a plurality of electrodes are provided, and the base
board is covered with a surface protective film. Using the flexible
board in such a manner makes possible to set the course of
recovering and transferring the toner freely. The drive circuit 8
for applying drive waveforms to the electrodes of the
recovery/transport member 7 applies multiple phase drive waveforms
having the phase patterns reverse to that of the waveforms from the
drive circuit 3 so as to transport the charged toner in the
direction reverse to the transport direction on the transfer board
1.
Next, the operation and function of transfer board 1 are described.
The recovery/transport member 7 also operates in similar to the
transfer board 1, but the recovery/transport member 7 functions
mainly as a transfer member.
When the drive circuit 3 applies drive waveforms of n phases to a
plurality of the electrodes 12 of the transfer board 1, the
electrodes 12 generate phase-shifting fields (traveling wave
fields), which either repel or attract respective grains of charged
powder on the transfer board 1. As a result, the powder is
transferred as it hops in the transporting direction of the
electric fields.
For example, as shown in FIG. 4, respective pulse drive waveforms
Va, Vb, and Vc, each of which shifts between the ground potential
of G (0 V) and a positive voltage, are applied by the drive circuit
to the electrodes 12 of the transfer board 1 in such a way that the
applying timing of each waveform is shifted to each other.
At a given moment, as shown in FIG. 5, when a negatively charged
grain of the toner T is on the transfer board 1 as the pulse drive
waveform is applied to a series of the electrodes 12 of the
transfer board 1 to give them the potential status of shown in FIG.
5, the negatively charged grain of toner T is attracted to the
electrode 12 with a positive potential.
When another waveform is applied according to a prescribed timing,
the potential status of the electrodes becomes 2 as shown in FIG.
5, where a repulsive force from the electrode 2 of "G" on the left
and an attractive force from the electrode 12 with a positive
potential on the right act together on the negatively charged grain
of toner T. As a result, the grain of toner T moves to the positive
electrode 12. Then, another waveform is applied according to a
prescribed timing, the potential status of the electrodes becomes 3
as shown in FIG. 5, where a repulsive force and an attractive force
act together on the negatively charged grain of toner T as in the
case of 2, moving the grain of toner T further to another positive
electrode 12.
As described above, when the multiphase drive waveforms with
shifting voltage are applied to a plurality of the electrodes 12,
the traveling waveform fields are generated on the transfer board
1, and the negatively charged toner T is transferred as it hops in
the transporting direction of the traveling waveform fields. It
will be appreciated that when the toner is positively charged,
reversing the shifting pattern of the drive waveforms brings the
same result as described above.
FIG. 6(a) shows a state that the negatively charged grains of toner
T are on the transfer board 1 when the electrodes A to F have no
potential (G). When the electrodes A and D become positive, as
shown in FIG. 6(b), the negatively charged grains of toner T are
attracted to the electrodes A, D and move onto them. Then,
according to the prescribed timing, the voltage of both electrodes
A, D become zero, as shown in FIG. 6(c), while the electrodes B, E
become positive. At this moment, the grains of toner T on the
electrodes A, D are repelled by the electrodes A, D and attracted
to the electrodes B, E, simultaneously, thus transferred to the
electrodes B, E. Then, at another shift of waveforms, the voltage
of both electrodes B, E become zero, as shown in FIG. 6(d), while
the electrodes C, F become positive. At this moment, the grains of
toner T on the electrodes B, E are repelled by the electrodes B, E
and attracted to the electrodes C, F, simultaneously, thus
transferred to the electrodes C, F. In this manner, the negatively
charged grains of toner are sequentially transferred to the right,
as shown in FIG. 6, by the traveling waveform fields.
The multiphase (3 phase) drive waveforms applied to the electrodes
of the transfer board 1 is described in detail. First, the relation
between the polarity of voltage applied to the electrodes and the
moving direction of the charged toner (powder) is described. When
the toner is negatively charged and the applied voltage is zero or
positive, the grains of toner jump in the reverse direction to that
of an electric line of force heading from a positive electrode to
an electrode of zero voltage. When the toner is positively charged,
the grains of toner jump in the same direction of the electric line
of force.
In FIG. 7 shows grains of toner on the electrode (B phase
electrode) to which B phase pulse (drive waveform Vb) is applied.
The behavior of the toner to an applying voltage pulse duty is
described using FIG. 7. When the negatively charged grains of toner
T are attracted to the B phase electrode while it is positive, the
grains of toner T start jumping in the reverse direction to that of
an electric line of force heading from a positive electrode to the
B phase electrode at the point that the voltage of the B phase
electrode is shifted to zero.
When the traveling waveform fields are generated by applying pulse
voltage (drive waveforms) of n phase (n stands for a natural number
of 3 or more) to each electrode, the positive voltage applying duty
of applied voltage pulse is set in such a way that a voltage
applying time per one phase is less than {repetition frequency
time.times.(n-1)/n}. In this manner, transfer and hopping of the
toner can be made more effectively.
For example, when three phases of drive waveforms A, B, C are
applied and the voltage applying time t a of each phase is set to
about 67% of the repetition frequency time t f, as shown in FIG. 8,
both A phase and C phase come to positive when B phase come to zero
voltage. Therefore, an electric field distribution given by a
series of electrode of A phase, of B phase, and of C phase is
symmetrical with respect to the electrode of B phase, as shown in
FIG. 14.
As a result, grains of toner on the half side in the transfer
direction of the electrode of B phase are moved in the direction of
transfer and hopping, but grains of toner on the opposite half side
is moved in the reverse direction, which reduces the efficiency of
the transfer. Therefore, setting the voltage applying time t a for
each phase to less than about 67% of the repetition frequency time
t f prevents the decline of transfer efficiency when three-phase
drive waveforms are used. When four-phase drive waveforms are used,
setting the voltage applying time for each phase to less than about
75% of the repetition frequency time prevents the decline of
transfer efficiency. For a purpose of making grains of toner jump
straight up from the electrode (less priority to the transfer),
setting the voltage applying time for each phase t a to less than
about 67% of the repetition frequency time t f will make the grains
of toner hop in the most effective manner.
FIG. 9 shows a case where the drive waveforms of three phases of A,
B, C are applied and the voltage applying time t a for each phase
is set to about 33% of the repetition frequency time t f, that is,
set to {repetition frequency time/n}. In this setting, at the
moment when the applied voltage of the electrode of B phase comes
to zero, the electrode of A phase comes to zero voltage and the
electrode of C phase comes to positive, thus the transporting
direction of powder becomes A to C. Therefore, the grains of toner
on the electrode of B phase become under influence of an electric
field making the grains of toner repelled by the electrode of A
phase and attracted to the electrode of C phase. Thus, the
efficiency of transfer and hopping is improved.
Therefore, in adjusting an applied voltage for each electrode, the
transfer efficiency can be improved when the voltage applying time
is set so as to make the electrode on the upstream side of
transporting direction repulsive and one on the downstream side
attractive when a given electrode is adjacent to the electrodes on
both sides of transfer direction. When a drive frequency is high,
setting the voltage applying time to more than {repetition
frequency time/n} to less than {repetition frequency
time.times.(n-1)/n} allows grains of toner on the given electrode
to easily gain an initial velocity, so that the repetition
frequency of transfer can be increased without reducing the
transfer efficiency, which is particularly advantageous for a high
speed transfer.
To achieve effective transfer and hopping, it is important to give
an initial velocity higher than a prescribed value to the powder
(toner) on the transfer board. For that purpose, an electric field
having a necessary strength is made to act on the toner on the
transfer board. The necessary strength is a strength needed to
allow each grain of toner break away from an absorption force, such
as a mirror image force, a van der Waals force and the like
capturing the grain according to its charge, and jump up.
The strength of a desirable electric field capable of giving a
force effective for transfer and hopping of the toner is more than
(5E+5) V/m. As a strength for eliminating a problem of absorption,
more than (1 E+6) V/m is desirable. Further, as a more desirable
strength to give an enough force, more than (2E+6) V/m is
desirable. When the grains of toner gaining an enough velocity from
an electric field having this strength move to a distance where the
influence of the field does not reach, the efficiency of transfer
and hopping is hardly affected even when the voltage relation, as
described for A, B, and C phases above, between a given electrode
and the adjacent positive electrodes on the downstream and the
adjacent electrode of zero voltage on the upstream comes to
collapse.
For example, when a voltage of 100 V is applied to the electrode,
the effect of field from the electrode becomes almost none at the
point 50 .mu.m above the electrode. Besides, the strength of field
is reduced to 1/5 at the point 30 .mu.m above the surface of the
electrode. Therefore, when a grain of toner accelerated to jump
upward has an average velocity of 0.3 to 1 m/sec, it takes 30 to
100 .mu.sec for the grain to travel through the distance of 30
.mu.m to reach the point where the strength of field declines to
1/5.
Therefore, it is desirable to set a voltage applying time of more
than 30 .mu.sec to apply a voltage to a given electrode of a
specific phase for repelling the powder, to the adjacent electrode
on the upstream for repelling, and to the adjacent electrode on the
downstream for attracting, simultaneously. In the above example
shown in FIG. 7, more than 30 .mu.sec of the voltage applying time
makes the upstream side adjacent electrode (electrode of A phase)
zero voltage and the downstream side adjacent electrode (electrode
of C phase) positive against the electrode of B phase. The voltage
applying time described above is a narrower condition for a
positive voltage applying pulse duty.
Next, a description is to be made for the width L of a plurality of
the electrodes 12 of the transfer board 1, on which the toner
(powder) is transferred as it hop, the space R between the
electrodes, the shape of drive waveforms, and the surface
protective layer 13. The width L of electrodes and the space R
between the electrodes substantially affects the transfer
efficiency and hopping efficiency of the powder (toner).
The grains of toner between electrodes are moved along the surface
of the board to the adjacent electrode due to electric fields
formed horizontally. Meanwhile, most of the grains of toner on the
electrode jump upward from the board surface with a given initial
velocity at least having a vertical component.
The grains of toner near the end of electrode jump across the
adjacent electrode as they move. Therefore, when the width L of
electrodes is wide, the number of the grains of toner on the
electrodes increase, so the grains of toner to make a long leap
increase since they jump across a wide electrode, thus improving
the transfer efficiency. However, a too large width of electrodes
leads to a decrease of the strength of an electric field near the
centers of electrodes, allowing the grains of toner to stick to the
electrodes, thus reducing the transfer efficiency. The inventor
found an appropriate width of the electrode for enabling an
effective transfer and hopping of powder at a low voltage.
The space R between electrodes determines the strength of electric
field between the electrodes because the strength of electric field
changes according to the relation between a distance and an applied
voltage. The narrower the space R is, the stronger the electric
field is, so it becomes easy for grains of toner to acquire an
initial velocity for the transfer and hopping when the space R is
narrow. However, the moving distance of grains of toner traveling
from electrode to electrode at one leap get shorter if the space R
is narrower. In such a case, the transfer efficiency cannot be
improved unless the drive frequency is increased. In solving this
problem, the inventor also found an appropriate space between the
electrodes for enabling an effective transfer and hopping of powder
at a low voltage.
The thickness of a protective layer covering the surface of
electrode affects the strength of electric fields on the surface of
electrode. Particularly, the electric line of force of vertical
component is strongly affected in determining the efficiency of
hopping.
Therefore, it is necessary to set an appropriate relation among the
width of electrodes, the space between electrodes, and the
thickness of the surface protective layer in order to solve the
problem of toner absorption on the electrode surface and enable the
effective transfer at a low voltage.
When the width L of electrodes is set to the same size as that of
the diameter of grains of toner (diameter of grains of powder), the
width L is the minimum size for transferring or hopping at least
one grain of toner. If the width L is narrower than the above size,
the electric field acting on the grain of toner becomes weaker,
which leads to less force of transfer and jumping, thus it becomes
difficult to put the electrodes in practical use.
As the width L go wider, the electric line of force come to incline
in the transfer direction (horizontal direction), especially near
the center of the space above the electrode, generating an area
where a vertical electric field is weak, thus reducing the force
for hopping the grains of toner. Too large width L may cause the
grains of toner to deposit on the electrode as an absorption force
capturing the grains according to their charge, such as a mirror
image force, a van der Waals force, and an absorption force caused
by water content, surpasses the vertical component of the grains of
toner.
In consideration for transfer and hopping, it is concluded that the
width L for allowing 20 grains of toner to be positioned on the
electrode will suppress the absorption, making possible to carry
out an effective transfer and hopping with given drive waveforms
having a low voltage of about 100 V. The width L wider than the
above size will form an area where the absorption occurs over the
electrode. In this case, for example, when the average grain
diameter of toner is 5 .mu.m, the width L is set to 5 .mu.m to 100
.mu.m.
A more desirable range of the width L for effective transfer by
drive waveforms having an applied voltage of lower than 100 V is
the range 2 to 10 times the average grain diameter of powder. By
setting the width L within this range, the decrease of the strength
of electric field near the center of the electrode surface can be
suppressed to the ratio of 1/3 or less, and the decrease of the
hopping efficiency becomes the ratio of 10% or less, thus a sharp
decline of the transfer efficiency can be avoided. In this case,
for example, when the average grain diameter of toner is 5 .mu.m,
the width L is set to 10 .mu.m to 50 .mu.m.
Further desirable width L of electrodes is the range 2 times to 6
times the average grain diameter of powder. In this case, for
example, when the average grain diameter of toner is 5 .mu.m, the
width L is set to 10 .mu.m to 30 .mu.m. It has proved that setting
the width L within this range substantially improves the transfer
efficiency.
A test has been conducted in the condition as shown in FIG. 10,
where the width L of the electrode 12 on the transfer board 1 is 30
.mu.m, the space R between electrodes is 30 .mu.m, the thickness of
the electrode 12 is 5 .mu.m, the thickness of the protective layer
13 is 0.1 .mu.m, and each voltage applied to adjacent two
electrodes 12, 12 is +100 V and zero. In this condition, the
strength of a transfer field TE and a hopping field HE for the
width L and the space R are measured, respectively. The result of
the measurement is shown in FIGS. 11 and 12.
Each appraisal data is a combined result from simulations,
measurements, and observations of the behavior of the grains of
toner using a high speed video. Though only two electrodes 12 are
shown in FIG. 10 for describing the detailed behavior of the grain
of toner, actual simulations and tests are conducted on an area
including substantial number of electrodes. The grain diameter T of
toner is 8 .mu.m, and the charge of one grain is -20 .mu.C/g.
The field strength as shown in FIGS. 11 and 12 is the field
strength value of a typical point on the surface of the electrode.
A typical point TEa in a transfer field TE is the point 5 .mu.m
above the end of electrode, as shown in FIG. 10, and a typical
point HEa in a hopping field HE is the point 5 .mu.m above the
center of electrode, as shown in FIG. 10. The typical point TEa
represents the spot where the electric field force acting on the
grain of toner is strongest in the direction of abscissa, while the
typical point HEa represents the spot where the electric field
force is strongest in the direction of ordinate.
According to FIGS. 11 and 12, it is found that the strength of
electric field capable of giving a force effective for transfer and
hopping of the toner is more than (5E+5) V/m. As the strength for
eliminating a problem of absorption, more than (1 E+6) V/m is
desirable. Further, as a more desirable strength to give an enough
force, more than (2E+6) V/m is desirable.
Since the electric field strength in the transfer direction
declines as the space R between electrodes becomes wider, it is
necessary to set the space R, as a value corresponding to the above
range of field strength, within a range of 1 to 20 times the
average grain diameter of toner, or desirably of 2 to 10 times, or
more desirably of 2 to 6 times.
As indicated in FIG. 12, the hopping efficiency also decreases as
the space R becomes wider. However, the space R within the range of
20 times the average grain diameter provides the hopping efficiency
for practical use. When the width R is over the above range, the
absorption force of grains of toner increases to the extent that
cannot be neglected, capturing some grains of toner to prevent them
from jumping. Therefore, the space R between electrodes must be 20
times or less the average grain diameter of toner.
As described heretofore, the electric field strength in the
direction of ordinate is determined by the width L of electrodes
and the space R between electrodes, and the narrower the width L
and space R are, the stronger the electric field strength is. The
electric field strength near the end of electrode in the direction
of abscissa is also determined by the space R between electrodes,
where the narrower the space R is, the stronger the electric field
strength is.
As described above, the width of electrode in the transporting
direction of the powder is set to 1to 20 times the average diameter
of the powder and the space between electrodes in the transporting
direction of the powder is set to also 1to 20 times the average
diameter of the powder. In this manner, it is possible to make an
electrostatic force of enough strength act on charged grains of the
powder on or between the electrodes so that the grains of powder
beak away from an absorption force, such as mirror image force, van
der Waals force and the like, to be transferred or hop. Thus, the
deposition of powder can be prevented, and a stable and effective
transfer and hopping of powder can be made at a low voltage.
According to the inventor's study, the transfer and hopping in the
above electrode constitution has proved to be effective when the
average diameter of toner is 2 to 10 .mu.m, and Q/m of negatively
charged toner is -3 to -40 .mu.C/g, more preferably -10 to -30
.mu.C/g, and Q/m of positively charged toner is +3 to +40 .mu.C/g,
more preferably +10 to +30 .mu.C/g.
Next, the shape of the drive waveforms applied to each electrode of
the transfer board is described. According to the constitution
shown in FIG. 10, the initial position and the horizontal travel
distance in a prescribed time (160 .mu.sec) of the grains of toner
has been measured under the condition that the average grain
diameter of toner is 8 .mu.m, Q/m of toner is -20 .mu.C/g, and
square (pulse) drive waveforms (a waveform having voltage value of
10 V and a waveform having voltage value of 50 V) and triangle
drive waveforms (maximum voltage value of 100 V) are applied, as
shown in FIG. 13. The result of measurement is shown in FIG.
14.
As indicated in FIG. 14, the square drive waveform of 50 V makes
the grains of toner travel at a shorter distance, compared to that
by the square drive waveform of 100 V. The triangle drive waveforms
having a rise-time and a downtime of 80 .mu.sec make the grains of
toner travel at the same distance as that by the square drive
waveform of 50 V.
As for the strength of the electric field forcing the toner on the
transfer board to travel and hop, the strength near the board,
which determines the initial velocity of the grains of toner, is
important. In other words, when an applied voltage is increased and
the electric field strength is enhanced after the grain of toner
has left far away from the board surface, the field does not
contribute to the transfer and hopping anymore, thus the transfer
efficiency is reduced.
For example, when the grain of toner accelerated to jump upward has
an average velocity of 0.3 to 1 m/sec, it takes 30 to 100 .mu.sec
for the grain to travel through the distance of 30 .mu.m to reach
the point where the strength of field declines to 1/5. Therefore,
in this case, the time constant of applied voltage of drive
waveform of 30 to 100 .mu.sec gives the grains of toner the initial
velocity, enabling the transfer and hopping of the toner.
FIG. 15 shows the result of a test in which the velocity of the
grains of toner in the hopping direction (hoping velocity) is
measured. In the test, the constitution shown in FIG. 10 is used,
and the average grain diameter of toner is 8 .mu.m, Q/m of the
grains of toner is -20 .mu.C/g, and square drive waveforms with a
high voltage value of 50 V, 10 V, and 150 V are applied. The FIG.
15 shows the velocity change of the grains of toner per 10 .mu.sec
and the height of the grains of toner from the electrode. The test
result shows that the grains of toner reaches the height of almost
100 .mu.m after a prescribed time (160 .mu.sec) has passed.
The drive waveform is not limited to square (pulse) drive waveform,
but other drive waveform, such as a triangular wave having a time
constant, also enable the transfer and hopping move. Besides, a
sine wave having a time constant equal to that of the above
waveforms can also be put in practical use to enable the transfer
and hopping move.
Next, the surface protective layer 13 is described. By providing a
surface protective layer, an attachment of fine particles and the
like on the electrode surface is prevented so that the electrodes
are protected from fouling. The protective layer can keep the
surface of board in a good condition for transfer of the toner, can
prevent a creeping leak occurring under a highly moist environment,
and eliminates the fluctuation of Q/m to maintain the quantity of
charge of the grains of powder in a stable manner.
FIG. 16 shows the result of calculation of the electric field
strength in the direction of abscissa when the thickness of surface
protective layer is changed within a range of 0.1 to 80 .mu.m in
the constitution shown in FIG. 10.
The dielectric constant .di-elect cons. of the surface protective
layer is higher than that of air, where .epsilon.=more than 2. As
indicated in FIG. 16, when the film thickness of the surface
protective layer (the thickness of a film formed between the
surface of electrode and the surface of transfer board) is too
thick, the strength of the electric field acting on the toner on
the surface decreases. Under consideration for the elements of
transfer efficiency, moisture or temperature environment and the
like, a condition for the surface protective layer that can be put
in practical use without a problem of a low efficiency of transfer
move is that the thickness of the surface protective layer is 10
.mu.m or less, where 30 .mu.m of thickness will result in the loss
of transfer efficiency by 30%, and 5 .mu.m of thickness is more
desirable because the decrease of the efficiency can be suppressed
to less than several % at this thickness.
FIGS. 17 and 18 show examples of the electric field strength
affects the hopping on the electrode surface. FIG. 17 shows a case
where the thickness of the surface protective layer is set to 5
.mu.m, while FIG. 18 shows a case where the thickness of the
surface protective layer is set to 30 .mu.m. In both cases, the
width of electrodes is 30 .mu.m, the space between electrodes is 30
.mu.m, and the applied voltage is 0 V and 100 V.
As indicated in FIGS. 17 and 18, making the surface protective
layer thicker increases electric fields heading for the adjacent
electrode through the protective layer having a dielectric constant
higher than that of air. As a result, the vertical component of the
field is reduced, so that the thickness of the surface protective
layer reduces the strength of electric field acting on the grains
of toner on the surface.
Therefore, the electric line of force of vertical component, which
acts on the grains of toner to hop them, depends greatly on the
thickness of protective layer. The strength of electric field
capable of giving a force effective for hopping of the toner at a
low voltage of about 100 V is, as the strength eliminating a
problem of absorption, more than (1E+6) V/m. As a more desirable
strength to give an enough force, more than (2E+6) V/m is
desirable. To obtain electric fields of such ranges, the thickness
of protective layer must be 10 .mu.m or less, and more desirably 5
.mu.m or less.
It is desirable that the surface protective layer consist of a
material of which the resistivity is more than 10*E 6 .OMEGA.cm and
dielectric constant .epsilon. is more than 2.
As described above, it becomes possible to make the vertical
component of electric fields act strongly on the powder to improve
the efficiency of hopping by providing the surface protective layer
to cover the electrode surface and setting the thickness of the
layer to 10 .mu.m or less.
Next, the thickness of electrodes 12 is described. When a surface
protective layer of several .mu.m covering the electrode surface is
formed, uneven parts are formed on the surface of the transfer
board, corresponding to an area where the electrode is under the
protective layer and an area where no electrode is under the
protective layer. However, when each electrode is formed into a
thin layer of less than 3 .mu.m, the unevenness of the transfer
board surface can be offset and grains of powder (toner) having the
average diameter of about 5 .mu.m can be transferred smoothly.
Therefore, forming electrodes having each thickness of 3 .mu.m or
less makes possible to put the transfer board having the thin
surface protective layer to practical use without a need of a
flattening treatment for the transfer board surface. Since such a
transfer board has the surface protective layer, the decrease of
electric field strength for transfer and hopping of powder is
eliminated, and more effective transfer and hopping can be carried
out.
Next, specific examples of the above transfer board are described.
When the electrostatic transfer apparatus of this invention is used
for the image forming apparatus, a specific size of a transfer
board for the transfer and hopping is required. The transfer board
must be rectangular and is at least 21 cm long or more and 30 cm
wide or more, where fine patterns are formed on such a large area.
To that end, it is desirable to laminate a thin-layered electrode
and a thin protective film (surface protective layer) in order on a
base material (support board) to form the transfer board.
For example, when manufacturing a transfer board having a flexible
fine pitch thin-layered electrode, a polyimide base film having a
thickness of 20 to 100 .mu.m is used as a base material (support
board 11), and a film of 0.1 to 3 .mu.m thick consisting of Cu, Al,
Ni--Cr, or the like is formed on the base material by a vapor
deposition method. A base material of 30 to 60 cm wide can be
manufactured using a roll-to-roll machine, so mass productivity is
improved. A plurality of electrodes each having a width of 1 to 5
.mu.m are formed simultaneously in a bath line.
The vapor deposition method includes a sputtering method, an ion
plating method, a CVD (chemical vapor deposition) method, an ion
beam method. For example, when the electrodes are formed by the
sputtering method, a Cr film may be interposed between polymide
base film and the electrodes so that the adhesiveness between the
polyimide and the electrodes is improved. The adhesiveness can also
be improved by a plasma treatment or a primer treatment, which is
carried out as a pre-treatment.
As a manufacturing method other than the vapor deposition method,
electro-deposition method may also be employed for forming a
thin-layered electrode. In this method, first, electrodes are
formed on a polyimide base material through a non electrolytic
plating process. Then the base material is dipped in a tin chloride
bath, a lead chloride bath, and a nickel chloride bath in order to
form a substrate electrode. After that, the base material is
subjected to a electrolyte plating process in a nickel electrolytic
solution, where a nickel film of 1 to 3 .mu.m thick is formed in a
roll-to-roll process.
The base material coated with the nickel film is further subjected
to a series of processes of resist coating, patterning, and
etching, then the electrodes 12 are formed. When thin-layered
electrodes of 0.1 to 3 .mu.m thickness are to be formed,
fine-patterned electrodes, each of which has a width of 5 to 10
.mu.m and is arranged between a space of 5 to 10 .mu.m, can be
formed in a precise manner by a photolithography or an etching.
In forming the surface protective layer 13, a film of 0.5 to 2
.mu.m thick consisting of SiO.sub.2, TiO.sub.2 or the like is
formed by a sputtering method and the like. Or, manufactured
electrodes are coated with a PI (polyimide) film of 2 to 5 .mu.m
thick, which is the protective layer, by a roll coater or other
coating apparatus, then is baked to be finished. If PI is
insufficient as the protective layer, a SiO.sub.2 film or other
inorganic film of 0.1 to 2 .mu.m thick may be further formed on the
PI film by a sputtering method and the like.
The flexible transfer board having the constitution described above
can be attached on a cylindrical drum, or formed into a partially
bent shape.
As another example, it is possible to make a polyimide base film of
20 to 100 .mu.m thick as a base material (support board 11) and a
Cu film, a SUS film or the like, which is 10 to 20 .mu.m thick, is
formed on the base material as an electrode material. In this case,
a metal material is coated with a polyimide by a roll coater to
form a polymide film of 20 to 100 .mu.m thick, and the coated
material is baked. Then, the pattern of electrodes 12 is formed on
the metal material by a photolithography or etching, and the
surface of the electrodes 12 is coated with a polyimide layer,
which is the protective film 13. If there is a surface unevenness
corresponding to the thickness of the metal material electrodes of
10 to 20 .mu.m, a sub-flattening process is carried out, where an
allowable unevenness is included.
For example, when a spin-coating of a polyimide material or
polyurethane material, which has a viscosity of 50 to 10,000 cps,
or more desirably, of 100 to 300 cps, is carried out and the
material is left alone, the surface tension of the material
smoothes out the unevenness of the board, flattening the top
surface of the transfer board. The coated material is further
subjected to a heat treatment and is made into a stable protective
film.
In another example of further improving the strength of the
flexible transfer board, a material consisting of SUS, Al or the
like, which is 20 to 30 .mu.m thick, is used as a base material.
The base material is coated with a diluted polyimide material of 5
.mu.m thick by a roll coater, where the polyimide material is
provided as an insulating layer between the base material and the
electrode. The polyimide material is, for example, pre-baked for 30
minutes at 150.degree. and is post-baked for 60 minutes at
350.degree. to form a thin polyimide film, which comprises the
support board 11.
The support board 11 is subjected to a plasma treatment or a primer
treatment in order to improve the adhesiveness of the polyimide
film. Then, a thin electric layer of Ni--Cr of 0.1 to 2 .mu.m thick
is formed on the above support board 11 by a vapor deposition
method, and the fine patterned electrodes 12 described above are
formed by a photolithography or an etching. Further, the surface
protective layer 13 of 0.5 to 1 .mu.m thick consisting of
SiO.sub.2, TiO.sub.2 or the like is further formed on the
electrodes by a sputtering method to form a flexible transfer
board.
In this example, a metal material used as the base material for the
transfer board 1 is the same material as that of a cylindrical
drum, or the one whose linear expansion coefficient is almost
coincides with the cylindrical drum, when the transfer board 1 is
wound around the cylindrical drum. In this manner, it is possible
to prevent the shrinkage of the transfer board caused by the linear
expansion coefficient difference between the transfer board 1 and
the cylindrical drum at a given temperature. Besides, when the
transfer board is used for the developing part of the image forming
apparatus, the base material consisting of SUS, Al or the like can
be used as a bias electrode between a photo sensitive body.
The transfer board 1 manufactured as described above is flexible so
that it can be wound around a cylindrical drum, or part of it can
be bent for more practical use. Besides, the mass production of
such a transfer board is possible using a roll-to-roll process.
Thus, transfer boards having highly accurate fine pitch electrodes
can be manufactured at a low cost.
Each transfer board described above need to be provided with an
electrode commonly connected to each electrode for generating
traveling wave fields. In a case of two-phase fields, both
electrodes can be formed simultaneously. In a case of three-phase
fields, a jumping pattern is formed via an insulating layer for one
phase.
Next, the relation between the charge polarity of traveling powder
and the material for the top layer of surface protective layer is
described. The top layer of surface protective layer means the
surface protective layer itself when the surface protective layer
consists of a single layer, while the top layer refers to the layer
forming the surface in contact with the powder when the surface
protective layer comprising a plurality of layers.
For the transfer of toner used for the image forming apparatus, a
melting temperature and transparency is considered in selecting a
resin material constituting 80% of the toner. Generally,
styrene-acrylate copolymer, polyester resin, epoxy resin, polyole
resin or the like is selected. Such a resin has an effect on the
charge characteristic of the toner, and a charge control agent is
added to the resin to control the quantity of charge. As a charge
control agent for black toner (BK), for example, nigrosine die or
fourth-ammonium salt class is used for positively charged toner,
while azo-containing metal complex or salicylic acid metal complex
is used for negatively charged toner. As a charge control agent for
color toner, for example, fourth-ammonium salt class or imidazole
complex class is used for positively charged toner, while salicylic
acid metal complex, salt class, or organic boron salt class is used
for negatively charged toner.
The toner comes in contact with and is separated from the surface
protective layer repeatedly while it is transferred and hop on the
transfer board by phase-shifting fields (traveling wave fields). As
a result, the toner receives the effect of a friction charge. The
quantity and polarity of friction charge depends on the charge
series of materials causing friction.
In this case, the charge quantity of the toner is kept at a
saturation quantity of charge that is determined mainly by the
charge control agent, or a little less. In this manner, the
efficiency of transfer, hopping, and photosensitive phenomenon can
be improved.
When the charge polarity of toner is negative, it is desirable to
use, as a material forming the top layer of surface protective
layer, a material positioned near the material of the charge
control agent (if the area for transfer and hoping is small) in the
order in the friction charge series, or a material positioned on
the positive side in the friction charge series. For example, when
the charge control agent is the salicylic acid metal complex, it is
desirable to use a polyamide material, such as polyamide (nylon)
66, nylon 11 and the like.
When the charge polarity of toner is positive, it is desirable to
use, as a material forming the top layer of surface protective
layer, a material positioned near the material of the charge
control agency (if the area for transfer and hoping is small) in
the order in the friction charge series, or a material positioned
on the negative side in the friction charge series. For example,
when the charge control agent is the fourth-ammonium salt class, it
is desirable to use a material positioned near fourth-ammonium salt
in the friction charge series, or a Teflon (registered trademark)
material, such as fluorine.
Next, the operation of the classifier constituted as described
above is described referring to FIG. 19 and other drawings. As
shown in FIG. 19, when the toner T charged by the charging brush 5
is supplied to the transfer board 1, the toner T is transferred on
the transfer board 1 in the arrowed direction as it hops. During
the transfer, each grain of toner acts differently on the electric
fields according to the strength of the fields generated by the
electrodes 12, because the mass and the quantity of charge of each
grain of toner T varies. As a result, some grains of toner Th make
a great hop and are transferred on the transfer board 1, and other
grains of toner Tl make a small hop or no hop at all and are
transferred as grains of toner Th, Tl respond to the strength of
the generated electric field. Although the extent of hopping
varies, the grains of toner Th and Tl are cited as a typical
example for two patterns of hopping for further description.
The grains of toner Th, Tl are transferred on the transfer bard 1
as they hop to the vicinity of the opposite roller 2, where a bias
voltage (positive) having the polarity reverse to the charge
polarity of the toner T (negative) has been applied to the opposite
roller 2. Then, the grains of toner Th hopping high on the transfer
board 1 are attracted to the opposite roller by its electric field
and are transported to the opposite roller 2, then are attached to
the surface thereof. The attached grains of toner Th is moved via
the rotation of the opposite roller 2 to a blade 8, where the
grains of toner Th are removed from the surface of the opposite
roller 2 and are sent to a storing part or a developing means,
which are not illustrated.
Meanwhile, the grains of toner Tl, which hop low or do not hop on
the transfer board 1, receive almost no influence of the electric
field generated by the opposite roller 2. Therefore, the grains of
toner Tl are keep transferred along the transfer board surface to
reach the other end of the transfer board 1, where the grains of
toner Tl are collected by the collecting electrode 6 and are
dropped on the recovery member 7. Then, the grains of toner Tl are
transferred again toward the charged brush 5 by traveling wave
fields form the recovery member 7. The charged brush 5 recharges
the grains of toner Tl, supplying them again to the transfer board
1.
Therefore, the toner T transferred on the transfer board 1 is
separated (classified) into the grains of toner Th and the grains
of toner Tl.
As described above, the extent of hopping (height of hopping) of
the toner T depends on a drive voltage given to the electrodes of
the transfer board 1 (generated electric fields). However, the
extent of hopping of the toner T depends also on the
characteristics of grains of toner and the characteristics within a
certain range allow the grains of toner Th to reach the opposite
roller 2 and stick to the surface thereof. The grains of toner
having a small mass, a great charge, or a large q/m make a great
jump (hop) on the transfer board 1. Accordingly, grains of toner
hopping high on the transfer board 1 are transported and attached
to the opposite roller 2, and other grains of toner are kept
transferred along the surface of the transfer board 1. In this
manner, the classification, or separation, of toner can be made
according to the characteristic differences of grains of toner.
The inventors have conducted a classification test of toner in the
constitution shown in FIG. 20. In the test, the toner is charged by
a charging means 5 using a magnet roller on one end of the transfer
board 1, from which the toner is supplied. The opposite roller 2 is
made opposite to the transfer surface of the transfer board 1
consisting of an aluminum roller, where the distance between the
transfer surface and the opposite roller 2 is 2 mm. The opposite
roller 2 is provided with a bias power source 4, from which a bias
voltage of DC 40 V and DC 20 V is selectively applied.
The relation between the applied voltage of roller and the quantity
of charge/mass (.mu.C/g) of grains of toner attached to the
opposite roller 2 is shown in FIG. 21. A bias voltage VB is changed
sequentially between 40 V and 20 V so that the repeatability of
results is assessed.
When the bias voltage of 40 V is applied to the opposite roller 2,
90% of the grains of toner having the -Q/M (Quantity of
charge/Mass) distribution shown in FIG. 22(a) is attached to the
opposite roller 2, and the charge of attached grains of toner is
about -8.8 to -9.2 (.mu.C/g), as shown in FIG. 21.
When the bias voltage of 20 V is applied to the opposite roller 2,
50% of the grains of toner having the -Q/M (Quantity of
charge/Mass) distribution show in FIG. 22(b) is attached to the
opposite roller 2, and the charge of attached grains of toner is
about -11 (.mu.C/g), as shown in FIG. 21. The charge of grains of
toner remains on the transfer bard 1 is about -8.6 (.mu.C/g), as
shown in FIG. 21.
The charge quantity of grain of toner attached to the opposite
roller 2 is measured by a suck-in method.
While raising the bias voltage VB for the opposite roller 2 makes
grains of toner having a low Q/M transported and attached to the
opposite roller 2, setting a proper bias voltage VB makes possible
to classify only the grains of toner having a high Q/M to be
transported and attached to the opposite roller 2.
As described above, when the classifier comprises the transfer
member having a plurality of electrodes for generating the electric
fields for transporting powder while transferring and hopping the
powder by an electrostatic force, and the opposite member to which
the powder transferred on the transfer member is transported and
attached, the opposite member being almost opposite to the transfer
member, the powder can be classified accurately and sequentially by
the classifier of a simple constitution. In this case, providing
the rotary opposite roller as the opposite member simplifies the
constitution of the opposite member.
As described in this embodiment, the grains of toner that has been
not transported and attached (captured) to the opposite roller 2
and transferred to the end of the transfer board 1 are collected by
the collecting electrode 6. The collected grains of toner are then
transferred on the recovery member 7 in the reverse direction to be
transferred back to the charging means 5, where collected grains of
toner are recharged. The recharged grains of toner are sent to the
transfer board 1 again, where the opposite roller 2 captures the
grains of toner having required quantity of charge and mass again.
Therefore, it is possible to obtain grains of toner having almost
uniform characteristic in a sequential manner.
Therefore, the powder can be classified accurately and sequentially
using the classifier of a simple constitution, in which powder is
transported while it is transferred and hopped by an electrostatic
force, and the powder is classified by providing a member to which
the powder transferred and hopped is transported and attached by an
electric field. As described later, it is not necessary that the
member for generating the electric field for transport and
attachment of powder and the member to which the powder is
transported and attached is the same.
As in the case of the first embodiment, the description of the
following embodiments are made concerning the classification of
negatively charged toner. When positively charged toner is
classified, the polarity of bias voltage is set reverse to that for
negatively charged toner.
Next, the second embodiment of the classifier of this invention is
described referring to FIG. 23, which is the schematic block
diagram of the classifier. In the classifier, three opposite
rollers 2,2,2 opposite to the transfer board 1 are arranged in the
transfer direction, respectively. A bias voltage VB1 from a bias
power source 41 is applied to the opposite roller 2 on the upstream
side, a bias voltage VB2 from a bias power source 42 is applied to
the opposite roller 2 in the middle, and a bias voltage VB3 from a
bias power source 43 is applied to the opposite roller 2 on the
downstream side (VB1<VB2<VB3).
With this arrangement, grains of toner having a large quantity of
charge per mass (q/m) among the toner transferred on the transfer
board 1 are transported and attached to the opposite roller 2 on
the upstream side, grains of toner having a middle quantity of
charge per mass (q/m) among the toner transferred on the transfer
board 1 are transported and attached to the opposite roller 2 on
the middle side, and grains of toner having a small quantity of
charge per mass (q/m) among the toner transferred on the transfer
board 1 are transported and attached to the opposite roller 2 on
the downstream side.
Since each opposite roller 2 generates an electric field of
different strength, each grains of toner having different quantity
of charge per mass (q/m) are transported and attached sequentially
to each opposite roller 2 according to the large to small size of
quantity of charge per mass (q/m) corresponding to the electric
field strength from the upstream to the downstream. As a result,
the toner are classified and captured in three steps. (The
classification is described as four step process if grains of toner
transferred through to the end of the transfer board 1 are
included.)
Next, the third embodiment of the classifier of this invention is
described referring to FIG. 24, which is the schematic block
diagram of the classifier. The classifier of this embodiment is
provided with an opposite transfer board 21, part of whose transfer
surface, which is an opposite member, is made almost opposite to
the transfer board 1. The constitution of the opposite transfer
board 21 is essentially the same as that of the transfer board 1,
and the opposite transfer board 21 is provided with a drive circuit
23, which applies drive waveforms Pv3 for generating traveling wave
fields to respective electrodes 12 of the opposite transfer board
21. A collecting electrode 24 for collecting part of classified
toner and a gutter 25 for taking in the collected toner are
arranged on the transfer end of the opposite transfer board 21.
It is desirable that the setting of the drive waveforms (drive
voltage) and the spaces between electrodes for the opposite
transfer board 21 are made so as to suppress the hopping of toner
during the transfer on the opposite transfer board 21 as much as
possible.
The opposite transfer board 21 is also provided with a bias
electrode 15. This electrode 15 is supplied with a bias voltage for
generating an electric field for attracting the toner hopping on
the transfer board 1 and transporting it to the opposite transfer
board 21. A bias power source 4 applies a bias voltage VB to the
bias electrode 15.
In this constitution, among the charged toner T transported while
being transferred and hopped on the transfer board 1, grains of the
toner T hopping high, having a large quantity of charge, or having
a small mass are attracted to the electric field generated by the
bias electrode 15 supplied with the voltage from the bias power
source 4 of the opposite transfer board 21. The attracted grains of
toner T are transported and attached to the opposite transfer board
21, thus classified.
The classified grains of toner T transported and attached to the
opposite transfer board 21 are then transferred by the traveling
wave fields generated on the opposite transfer board 21 to the
collecting electrode 24, and are stored in the gutter 25 (or may be
sent to a developing means as described later).
The opposite transfer board 21 comprises the part opposite to the
transfer board 1 (the part on which the bias electrode 15 is
arranged), which functions as an opposite member, and the part not
opposite to the transfer board 1, which functions as a transfer
member. Therefore, the opposite member and the transfer member are
integrally formed to constitute the opposite transfer board 21,
which is a single board. Besides, the support board 11 of the
opposite transfer board 21 is made of a flexible board, so that
prescribed classified grains of toner can be transferred in a
desired direction.
Next, the fourth embodiment of the classifier of this invention is
described referring to FIG. 25, which is the schematic block
diagram of the classifier of this embodiment. The classifier of
this embodiment is provided with three opposite transfer boards 21,
21, 21,which are opposite to the transfer board 1 and arranged in
perpendicular to the transfer direction of toner T on the transfer
board 1. The bias voltage VB1 from the bias power source 41 is
applied to the opposite transfer board 21 on the upstream side, a
bias voltage VB2 from a bias power source 42 is applied to the
opposite transfer board 21 in the middle, and a bias voltage VB3
from a bias power source 43 is applied to the opposite transfer
board 21 on the downstream side (VB1<VB2<VB3).
With this arrangement, grains of toner having a large quantity of
charge per mass (q/m) among the toner transferred on the transfer
board 1 are transported and attached to the opposite transfer board
21 on the upstream side, grains of toner having a middle quantity
of charge per mass (q/m) among the toner transferred on the
transfer board 1 are transported and attached to the opposite
transfer board 21 on the middle side, and grains of toner having a
small quantity of charge per mass (q/m) among the toner transferred
on the transfer board 1 are transported and attached to the
opposite transfer board 21 on the downstream side.
Since each opposite transfer board 21 generates an electric field
of different strength, each grains of toner having different
quantity of charge per mass (q/m) are transported and attached
sequentially to each opposite transfer board 21 according to the
large to small size of quantity of charge per mass (q/m)
corresponding to the electric field strength from the upstream to
the downstream. As a result, the toner are classified and captured
in three steps. Besides, since the opposite transfer boards 21 are
arranged in perpendicular to the transfer board 1 in this case, the
transfer direction of the classified toner becomes perpendicular to
the transfer direction of the transfer board 1.
Next, the fifth embodiment of the classifier of this invention is
described referring to FIG. 26, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
an opposite belt 31 as the opposite member, part of which is
opposite to the transfer board 1, is arranged in almost parallel to
the transfer board 1. The opposite belt 31 consists of an endless
belt, stretched across rotating rollers 32, 33, and is circulated
on the rollers in the arrow direction. It is desirable to provide a
metal film or a laminated films consisting of an organic film and a
metal film on the surface of the opposite belt 31, because a bias
voltage is applied to the opposite belt 31.
A bias voltage VB is applied from the bias power source 4 to the
opposite belt 31. A blade 34 for separating the toner on the
opposite belt 31 and a gutter 35 for storing the toner separated by
the blade 34 are arranged near the periphery of the roller 32 of
the opposite belt 31.
In this constitution, among the charged toner T transported while
being transferred and hopped on the transfer board 1, grains of the
toner T which hop high, have a large quantity of charge, or a small
mass are attracted to the electric field generated by the bias
electrode 15 supplied with the voltage from the bias power source 4
of the opposite belt 31. The attracted grains of toner T are
transported and attached to the opposite belt 31, thus
classified.
The classified grains of toner T transported and attached to the
opposite belt 31 are then transferred on the circulating opposite
belt 31 to the blade 34, where attached grains of toner T are
separated from the opposite belt 31, and are stored in the gutter
35 (or may be sent to a developing means as described later).
The opposite belt 31 comprises the part opposite to the transfer
board 1, which functions as the opposite member, and the part not
opposite to the transfer board 1, which functions as the transfer
member. Therefore, the opposite member and the transfer member are
integrally formed to constitute the opposite belt 3, which is a
single member.
In this embodiment, the toner can also be classified in three steps
by providing a plurality of opposite belts 31.
Next, the sixth embodiment of the classifier of this invention is
described referring to FIG. 27, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
the end part of the transfer surface of the opposite transfer board
21, which is the opposite member, is opposite to the transfer board
1 and the opposite transfer board 21 is inclined against the
transfer board 1 at an angle of .theta.. The most closest distance
d between the opposite transfer board 21and the transfer board 1 is
set within a range of 0.5 to 100 mm, and the angle .theta. is made
less than 45 degree. However, the values of distance d and the
angle .theta. are not limited to the above range.
In this constitution, among the charged toner T transported while
being transferred and hopped on the transfer board 1, grains of the
toner T which hop high, have a large quantity of charge, or a small
mass are attracted to the electric field generated by the bias
electrode 15 supplied with the voltage from the bias power source 4
of the opposite transfer board 21, as in the case of the third
embodiment. The attracted grains of toner T are transported and
attached to the opposite transfer board 21, thus classified. Then
classified grains of toner T are collected by a collecting
electrode 24 at the end of the opposite transfer board 21 and are
stored in a gutter 25.
The arrangement of this classifier may be changed in such a way
that the closest distance d between the transfer surface of the
transfer board 1 and the opposite transfer board 21 is changed from
5 to 100 mm, and the angle .theta. of the opposite transfer board
21 is changed from 0 degree to 45 degree, where the bias voltage VB
is also adjusted. When the distance d is small, thin-film-shaped
particle groups (groups of grains of the powder) can be captured
sequentially with an applied voltage of 20 to 300 V. When the
distance d is large, a large amount of thick-film-shaped particle
groups (groups of grains of the powder) can be captured
sequentially with an applied voltage of 100 to 2000 V.
Next, the seventh embodiment of the classifier of this invention is
described referring to FIG. 28, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
the end part of the opposite transfer board 21 having the bias
electrode 15 is the opposite member and is set almost parallel to
the transfer board 1, while the other part of the opposite transfer
board 21 is inclined against the transfer board 1 at an angle of
.theta.. The most closest distance d between the opposite transfer
board 21and the transfer board 1 is set within a range of 0.5 to
100 mm, and the angle .theta. is made less than 45 degree. However,
the values of distance d and the angle .theta. are not limited to
the above range.
The constitution of this embodiment provides the same effect
provided by the above sixth embodiment. However, when the whole
body of the opposite transfer board 21 is inclined, an edge effect
tends to occur on the part of the opposite transfer board 21 most
close to the transfer board 1,i.e., an edge, where the grains of
toner transported come to concentrate on the edge. In this
embodiment, the part to which the grains of toner are transported
and attached is arranged in almost parallel to the transfer board
1, so that occurring of the edge effect is prevented.
Next, the eighth embodiment of the classifier of this invention is
described referring to FIG. 29, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
the opposite belt 31 as the opposite member is inclined against the
transfer board 1 at an angle of .theta.. The most closest distance
d between the opposite belt 31 and the transfer board 1 is set
within a range of 0.5 to 10 mm, and the angle .theta. is made less
than 45 degree. However, the values of distance d and the angle
.theta. are not limited to the above range.
In this constitution, among the charged toner T transported while
being transferred and hopped on the transfer board 1, grains of the
toner T which hop high, have a large quantity of charge, or a small
mass are attracted to the electric field generated by the bias
electrode 15 supplied with the voltage from the bias power source 4
of the opposite belt 31, as in the case of the fifth embodiment.
The attracted grains of toner T are transported and attached to the
opposite belt 31, thus classified. Then classified grains of toner
T are separated from the surface of the belt 31 by the blade 34 as
the belt 31 circulates and are stored in the gutter 35.
The arrangement of this classifier may be changed in such a way
that the closest distance d between the transfer surface of the
transfer board 1 and the opposite belt 31 is changed from 5 to 100
mm, and the angle .theta. of the opposite belt 31 is changed from 0
degree to 45 degree, where the bias voltage VB is also adjusted.
When the distance d is small, thin-film-shaped particle groups
(groups of grains of the powder) can be captured sequentially with
an applied voltage of 20 to 300 V. When the distance d is large, a
large amount of thick-film-shaped particle groups (groups of grains
of the powder) can be captured sequentially with an applied voltage
of 100 to 2000 V.
Next, the ninth embodiment of the classifier of this invention is
described referring to FIG. 30, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
the transfer board 1 is arranged in an inclined position, and a
slit member 51 having slit holes 52a, 52b, 52c is set opposite to
the transfer board 1. The slit holes 52a, 52b, 52c are provided
with bias electrodes consisting of metal film 53a, 53b, 53c,
respectively. Each bias voltage VB1, VB2, VB3 from respective bias
power source 41, 42, 43 is applied to bias electrodes 53a, 53b,
53c, respectively.
Each slit hole 52a, 52b, 52c is provided with a corresponding
gutter 54a, 54b, 54c, to which bias voltage VB4, VB5, VB6, which is
higher than the bias voltage VB1, VB2, VB3, respectively, from bias
power source 55A, 55B, 55C is applied
The charged grains of toner T transported while they are hopped and
transferred on the transfer board 1 are attracted to electric
fields generated by the bias voltage VB1, VB2, VB3 according to
each quantity of charge or mass, and are transported toward the
slit hole 52a, 52b, 52c. As the grains of toner T approach the slit
holes 52a, 52b, 52c, the bias fields of the gutters 54a, 54b, 54c
act on the grains of toner T, making them pass through the slit
holes 52a, 52b, 52c to be captured by the gutters 54a, 54b, 54c. In
this case, the opposite member for generating the electric fields
for the transport and attachment of the grains of toner T on the
transfer board 1 is the slit member 51, but the grains of toner T
are actually transported and attached to the gutters 54a, 54b, 54c.
Therefore, the member for generating the electric fields for the
transport and attachment of the toner and the member to which the
toner is actually transported and attached is different in this
embodiment. As a member to which the toner is transported and
attached, a belt, roller, an electrostatic transfer board or the
like may be employed, instead of a gutter, for facilitating the
transfer of the toner.
In this embodiment, the toner transferred on the transfer board 1
can be classified in three steps as in the case of the second or
the fourth embodiment.
As shown in FIG. 31, the slit holes and bias electrodes of the slit
member 51 can be formed into various shapes, which are shown in
FIG. 31. For example, as shown in FIG. 31(a), a slit hole 52 is
square-shaped, and a bias electrode 53 is formed on the inner
surface of the slit hole 52. FIG. 31(b) shows a tapered slit hole
52, where the bias electrode 53 is formed on the inner surface of
the slit hole 52. FIG. 31(c) shows a slit hole 52 slant in the
transfer direction of the toner, where the bias electrode 53 is
formed on the inner surface of the slit hole 52.
Next, the tenth embodiment of the classifier of this invention is
described referring to FIG. 32, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
the transfer board 1 is arranged in an inclined position, and a
slit member 61 having slit holes 62a, 62b, 62c is set opposite to
the transfer board 1. On the outside of the slit member 61,
electrode wires 63a, 63b, 63c are arranged as the opposite member
to the transfer member 1, where the electrode wires 63a, 63b, 63c
correspond to the slit holes 62a, 62b, 62c, respectively. The bias
voltage VB1, VB2, VB3 from the bias power source 41, 42, 43 is
applied to each electrode wires 63a, 63b, 63c. It will be
appreciated that, in this specification, the term "electrode wire"
represents not only line electrode wires, but also includes
bar-shaped one (electrode bars), and the section of "electrode
wire" is not limited to circular-shape, but also includes
ellipse-shape and square-shape.
The electrode wire 63 may be provided as a single wire, as shown in
FIG. 33(a), or two or more than three of a plurality of wires, as
shown in FIG. 33(b). The outer periphery of the electrode wire 63
is sheathed with an insulating protective film 65, whose thickness
is, for example, 5 to 20 .mu.m. The insulating protective film 65
prevents a change of the quantity of charge of the toner occurring
when it sticks to the electrode wire 63.
By providing the insulating protective film 65 on the surface of
the electrode wire 63, the charge given to the powder is controlled
according to the conductivity, semi-conductivity, or insulating
property of the powder. When the powder comes in contact with the
board or the electrode wire 63 for attracting the powder and causes
a contact charge or a friction charge, a proper material of the
protective film is selected to match the charge order of powder
with that of the protective film. In this manner, the charge
characteristics and the quantity of charge of powder can be
controlled.
As a material forming the insulating protective film 65, when the
charge polarity of toner is negative, it is desirable to use a
material positioned near the material of the charge control agent
(if the area for transfer and hoping is small) in the order in the
friction charge series, or a material positioned on the positive
side in the friction charge series. For example, when the charge
control agent is a salicylic acid metal complex, it is desirable to
use a polyamide 66, polyamide 11, SiO.sub.2 and the like.
When the charge polarity of toner is positive, it is desirable to
use a material positioned near the material of the charge control
agency (if the area for transfer and hoping is small) in the order
in the friction charge series, or a material positioned on the
negative side in the friction charge series. For example, when the
charge control agent is a fourth ammonium salt class, it is
desirable to use a material near the fourth ammonium salt class in
the friction charge series or Teflon (registered trademark)
material, such as fluorine.
The classifier of this embodiment is also provided with gutters
64a, 64b, 64c for storing captured toner, gutters 64a, 64b, 64c
corresponding to the electrode wires 63a, 63b, 63c.
The charged grains of toner T transported while they are hopped and
transferred on the transfer board 1 are attracted to electric
fields generated by the bias voltage VB1, VB2, VB3 applied to the
electrode wires 63a, 63b, 63c according to each quantity of charge
or mass, and are transported toward the slit holes 62a, 62b, 62c,
then pass them through to stick to the electrode wires 63a, 63b,
63c, and finally stored in the gutter 54a, 54b, 54c.
Therefore, in this embodiment, the toner transferred on the
transfer board 1 can be classified in three steps as in the case of
the second or the fourth embodiment.
Next, the eleventh embodiment of the classifier of this invention
is described referring to FIG. 34, which is the schematic block
diagram of the classifier of this embodiment. In this classifier,
as in the case of the tenth embodiment, the transfer board 1 is
arranged in an inclined position, and a slit member 61 having slit
holes 62a, 62b, 62c is set opposite to the transfer board 1. On the
outside of the slit member 61, electrode wires 63a, 63b, 63c are
arranged as the opposite member to the transfer member 1, where the
electrode wires 63a, 63b, 63c correspond to the slit holes 62a,
62b, 62c, respectively. Each bias voltage VB11, VB12 and VB13 from
bias drive circuits 71, 72, 73 is applied to each electrode wire
63a, 63b and 63c.
The electrode wire 63 (63a, 63b, 63c) may be provided as a single
wire, or two or more than three of a plurality of wires, as
described before. The outer periphery of the electrode wire 63 is
sheathed with the insulating protective film 65 made of a selected
material having a proper charge order. The drive waveforms the bias
drive circuits 71, 72, 73 applied to the electrode wires 63a, 63b,
63c are sine waves, as shown in FIG. 35(a), bipolar pulse waves, as
shown in FIG. 35(b), or unipolar pulse waves, as shown in FIG.
35(c), where each drive waveform applied to each electrode is all
the same.
As in the case of the tenth embodiment, the charged grains of toner
T transported while they are hopped and transferred on the transfer
board 1 are attracted to electric fields generated by the bias
voltage VB1, VB2, VB3 applied to the electrode wires 63a, 63b, 63c
according to each quantity of charge or mass, and are transported
toward the slit holes 62a, 62b, 62c, then pass them through to
stick to the electrode wires 63a, 63b, 63c, and finally stored in
gutters 64a, 64b, 64c.
As described before, since the drive waveforms of sine waves,
bipolar waves, or unipolar waves from the bias drive circuits 71,
72, 73 are applied to the electrode wires 63a, 63b, 63c, there are
moments that the bias voltage is not applied to the electrode wires
63a, 63b, 63c. Upon cutting off of the bias voltage on the
electrode wires 63a, 63b, 63c, the electric fields disappear,
causing the toner sticking to the electrode wires 63a, 63b, 63c to
drop by its own weight.
Therefore, the constitution provided in this embodiment requires no
means for dropping the toner sticking to electrode wires 63a, 63b,
63c, such as forced vibration of the electrode wires 63a, 63b, 63c,
which is required for the tenth embodiment. Thus, a simpler
constitution of the classifier is provided in this embodiment.
Next, the twelfth embodiment of the classifier of this invention is
described referring to FIG. 36, which is the schematic block
diagram of an important element of the classifier of this
embodiment. In this classifier, two electrodes wires 63, 63 spaced
apart at a prescribed gap are provide for each slit hole 62a, 62b,
and 62c in the constitution of eleventh embodiment. A bias drive
circuit 74 applies a bias voltage VB of sine wave drive waveforms
to the electrodes wires 63, 63.
Two electrodes wires 63, 63 repeatedly attract and repel each other
as the sine wave drive waveforms are applied, thus vibrate. The
vibration shakes off the toner sticking to electrodes wires 63, so
that it becomes possible to remove the toner sticking to electrodes
wires 63 by arranging a simply constituted element.
Next, the thirteenth embodiment of the classifier of this invention
is described referring to FIGS. 37 and 38, where FIG. 37 is the
schematic block diagram of the classifier of this embodiment and
FIG. 38 is the enlarged detail of FIG. 37. The drawings of bias
power sources for respective electrodes and the like are partially
omitted.
In the classifier of this embodiment using the constitution of the
tenth embodiment, each slit hole 62a, 62b, and 62c is covered with
a metal films 81, which is provided with a bias power source 82
applying a bias voltage VB8 having the same polarity as charge
polarity of the toner to be classified (which is negative, so the
bias voltage is negative), as shown in FIG. 38. The electric field
generated by the bas voltage VB8 is made weaker than the electric
fields by the electrode wires 63.
The bias voltage VB8 prevents the negatively charged toner, which
passes through the slit holes 62a, 62b, 62c as it is attracted by
the electric fields generated by the electrode wires 63, from
sticking to the walls of the slit holes 62a, 62b, 62c or to the
surface of the slit member 1 opposite to the transfer board 1.
Therefore, it is possible to prevent the decrease of the transport
efficiency of powder due to the deposition or attachment of
classified powder on the slit or the opposite surface. It is also
possible to prevent the deterioration of the residence
characteristic of the grains of powder which occurs when the grains
of powder are left on the board for a long time.
Next, the fourteenth embodiment of the classifier of this invention
is described referring to FIGS. 39 and 40, where FIG. 39 is the
schematic block diagram of the classifier of this embodiment and
FIG. 40 is the plain view of the electrode wire lines shown in FIG.
38.
In this embodiment, the electrode wire line member 91 is provided
as the opposite member generating the electric fields for
transporting and attaching the toner on the transfer board 1 to the
electrode wire line member 91. As shown in FIG. 40, the electrode
wire line member 91 comprises a number of electrode wires 92
(including the electrode wire 63 and the insulating protective film
65) held by a flexible holding frame member 93, which makes
possible to deform the electrode wire line member 91 into a desired
shape, such as linear shape or curved shape.
One or a plurality of electrode wires 92 on the end of the
electrode wire line member 91 are made to be the opposite member
opposite to the transfer board 1, and the other electrode wires 92
are used as a transfer means. In this case, n-phase drive waveforms
Pv3 are applied to each electrode wire 92 of electrode wire line
member 91 to generate traveling wave fields on the surface of the
electrode wires 92, which forms the transfer part (transfer
means).
The electrode wires 92 of the electrode wire line member 91 form a
line of electrode wires set in a space, on which drive
phase-shafting fields are formed around every electrode wire
enabling a transfer of a large amount of the powder. It is
desirable to apply the n-phase drive waveforms Pv3 for transferring
the powder, mainly toner, to each electrode wire 92 of the
electrode wire line member 91.
With this arrangement, the charged grains of toner T transported
while they are hopped and transferred on the transfer board 1 are
attracted to electric fields generated by the one or a plurality of
electrode wires 92 of the electrode wire line member 91 opposed to
the transfer board 1, according to each quantity of charge or mass,
and are transported and attached to the electrode wires 92 of the
electrode wire line member 91. The attached grains of toner T are
transferred by the traveling wave fields generated by the electrode
wire line member 91, reaching the end of it, and are stored in a
gutter 94.
In this embodiment, the transfer course of classified toner can be
arranged more freely and the transfer volume of toner can be
increased by using the electrode wire line.
Next, the fifteenth embodiment of the classifier of this invention
is described referring to FIG. 41, which is the schematic block
diagram of the classifier of this embodiment. The classifier of
this embodiment is provided with the electrode wire line member 91
of the fourteenth embodiment, and a suction duct 96 is arranged at
the end of the electrode wire line member 91. The suction duct 96
sucks in the classified toner transferred by the traveling wave
fields generated by the electrode wires 92 of the electrode wire
line member 91 to transport the toner to a prescribed place.
In this embodiment, using the electrode wire line enables a more
freer arrangement of the transfer course of toner and increase the
transfer volume of toner, as in the case of the fourteenth
embodiment. With these advantages, the classifier of this
embodiment can also be utilized for a manufacturing process of
toner.
Next, the first embodiment of the developer of this invention
including the classifier is described referring to FIG. 42, which
is the schematic block diagram of the developer of this embodiment.
In this developer, classified almost uniform grains of toner are
attached to an electrostatic latent image formed on a
photosensitive drum 131, which is a latent image carrier, for
development. The photosensitive drum 131 may be substituted with a
belt-shape photosensitive body in this embodiment as well as the
following embodiments.
The developer comprises a toner hopper 111 for storing toner
supplied from a toner bottle and the like arranged outside, an
agitator 12 for agitating the toner in the toner hopper 111, a
toner supply/recovery member 113, a charging roller 113 for
charging the toner in the toner hopper 111 and sending them into a
toner supply member 7a, and a doctor blade 114 set in contact with
the periphery of charging roller 113. The developer further
includes a recovery member 7 consisting of a recovery member 7a,
i.e., the toner supply member 7a, and a sending member 7b for
sending the toner to the charging means 5, both of which are
supplied with drive waveforms applied by the drive circuit 8.
A slit member 121 having a plurality of slit holes 122, similar to
that of the tenth embodiment, is arranged in opposite to the
transfer board 1. Electrode wires 123 sheathed with a insulating
protective film are arranged in opposite to transfer board 1 and
corresponding to each slit hole 122, where each electrode wire 123
generates an electric field for transporting and attaching the
classified toner. The same bias voltage VB from a bias power source
124 is applied to each electrode wire 123 so as to classify the
grains of toner having almost same characteristics from the toner
hopping and being transferred on the transfer board 1.
Toner guide members 125 each corresponding to each electrode wire
123 are provided. The captured grains of toner are guided with the
guide members 125 to join on a toner guide members 126, from which
the captured grains of toner are supplied to a developing roller
132 that is a developing means for attaching the toner to an
electrostatic latent image formed on the photosensitive drum 131,
which is the latent image carrier. An AC voltage from an AC power
source 133 and DC voltage from a DC power source 132 are applied
across the photosensitive drum 131 and the developing roller 132 so
as to make the toner jump from the developing roller 132 to the
photosensitive drum 131 to develop the latent image.
The toner guide member 126 comprises a board similar to the
transfer board 1, which makes possible to send the toner to the
developing roller 132 without fail.
With the constitution described above, it becomes possible to
classify charged grains of toner having a large q/m and supply them
to the developing roller 132. As a result, the uniformity of the
toner for development is enhanced, so that the quality of
development is improved, thus the quality of images is improved.
Besides, the grains of toner having small q/m are not captured or
classified and are discharged from the transfer board 1, then sent
back again to the charging means 5 through the recovery means 5 and
are recharged. As a result, it is possible to make grains of toner
having a large q/m captured in a stable manner.
Since a plurality of electrode wires 123 (may be more than three),
which is the opposite member for generating electric fields for
classification, are provided in the developer of this embodiment,
it is possible to compensate a short supply of the toner to the
developing roller, so that the decrease of developing speed can be
prevented substantially.
Next, the second embodiment of the developer of this invention
including the classifier is described referring to FIG. 43, which
is the schematic block diagram of the developer of this embodiment.
In this developer, toner is classified into almost uniform grains
of toner using a classifier almost the same one of the sixth
embodiment. The classified toner is attached to an electrostatic
latent image on the photosensitive drum 131, which is the latent
image carrier, to develop the image.
In the developer of this embodiment, the toner T is fed from a
toner tank 141 to charging brushes 142, 143, which are in contact
with each other and rotate, causing friction to charge the toner,
which is then sent to the transfer board 1 to which an opposite
transfer board 221 is arranged in an inclined position. The
opposite transfer board 221 comprises a classifying part 221a
having the bias electrode 15, to which the bias voltage VB is
applied and the grains of toner having required characteristics are
transported and attached, as in the case of the sixth embodiment, a
transfer part 221b for transferring the attached grains of toner by
the traveling wave fields generated by the electrodes 12, and a
developing part 221c for hopping and transferring the toner near
the photosensitive drum 131, wherein the classifying part 221a, the
transfer part 221b, and the developing part 221c are integrally
formed. Therefore, the opposite transfer board 221, which is the
opposite means, also functions as the developing means.
With the constitution described above, it becomes possible to
classify charged grains of toner having a large q/m and supply them
to the developing part of the opposite transfer board 221. As a
result, the uniformity of the toner for development is enhanced, so
that the quality of development is improved, thus the quality of
images is improved. Besides, the grains of toner having small q/m
are not captured or classified and are discharged from the transfer
board 1, then sent back again to the charging brush 143 and the
like through the recovery means 7 and are recharged. As a result,
it is possible to make grains of toner having a large q/m captured
in a stable manner. The developing operation utilizing the
electrostatic transfer including hopping phenomenon is described in
detail later.
The constitution of the developer of this embodiment is made simple
by carrying out classifying of the toner, supplying of the toner to
the developing part, and hopping of the toner on the developing
part using the opposite transfer board only.
Next, the third embodiment of the developer of this invention
including the classifier is described referring to FIG. 44, which
is the schematic block diagram of the developer of this embodiment.
In this developer, toner is classified into almost uniform grains
of toner using a classifier almost the same one of the fifth
embodiment. The classified toner is attached to an electrostatic
latent image on the photosensitive drum 131, which is the latent
image carrier, to develop the image.
In this developer, the grains of toner having required
characteristics transferred and attached to the opposite belt 31
from the toner transferred and hopped on the transfer board 1. The
attached grains of toner are then sent to the developing part
opposite to the photosensitive drum 131 via the circulation of the
opposite belt 31, where the toner on the opposite belt 31 attached
to a latent image part by an electric field from the electrostatic
latent image. This development is a result of the contact between
the opposite belt 31 and the photosensitive drum 131, that is, the
opposite belt 31, which is the opposite means, also functions as
the developing means. Though the developer of this embodiment is
not provided with the blade 34, as different from the case of the
fifth embodiment, the blade 34 may be provided to drop the grains
of toner that has been not used for development to the collecting
electrode 6 so that they are recycled.
With the constitution described above, it becomes also possible for
the developer of this embodiment to classify charged grains of
toner having a large q/m and supply them from the opposite belt 31
to the developing part. As a result, the uniformity of the toner
for development is enhanced, so that the quality of development is
improved, thus the quality of images is improved. Besides, the
grains of toner having small q/m are not captured or classified and
are discharged from the transfer board 1, then sent back again to
the charging brush 143 and the like through the recovery member 7
and are recharged. Thus, it is possible to make grains of toner
having a large q/m captured and used for development in a stable
manner.
Next, the fourth embodiment of the developer of this invention
including the classifier is described referring to FIG. 45, which
is the schematic block diagram of the developer of this embodiment.
This developer is provided with a belt 153 stretched across rollers
151, 152 arranged above the transfer board 1. An opposite electrode
155 is arranged on the back of the part of the belt 153 opposite to
the transfer board 1, where the opposite electrode 155 functions as
the opposite member opposite to the transfer board 1. A bias
voltage VB from the bias power source 4 is applied to the opposite
electrode 155 to generate an electric field for transporting and
attaching the grains of toner having required characteristics among
the toner transferred and hopped on the transfer board 1. A bias
power source 156 is provided between the opposite electrode 155 and
the photosensitive drum 131, where the bias power source 156
applies the bias voltage VC higher than the bias voltage VB to the
opposite electrode 155. In this developer, the opposite member for
generating an electric field and the member to which the powder is
transported and attached are separately provided.
The grains of toner having the required quantity of charge and mass
among the toner transferred and hopped on the transfer board 1 are
attracted to the electric field from the opposite electrode 155,
and are transported and attached to the surface of the belt 153.
The attached grains of toner are sent onto the side where the belt
153 faces the photosensitive drum 131 via the circulation of the
belt 153, and are transported and attached to the latent image part
on the photosensitive drum 131 by a bias field formed across the
belt 153 and the photosensitive drum 131 and an electric field from
an electrostatic latent image, thus the image is developed.
With the constitution described above, it is possible for the
developer of this embodiment to classify charged grains of toner
having a large q/m, and transport and attach them to the belt 153,
then supply them to the developing part. As a result, the
uniformity of the toner for development is enhanced, so that the
quality of development is improved, thus the quality of images is
improved. Besides, the grains of toner having small q/m are not
captured or classified and are discharged from the transfer board
1, then sent back again to the charging brush 143 and the like
through the recovery member 7 and are recharged. Thus, it is
possible to make grains of toner having a large q/m captured and
used for development in a stable manner.
Next, the fourth embodiment of the developer of this invention
including the classifier is described referring to FIG. 46, which
is the schematic block diagram of the developer of this embodiment.
In this developer, toner is classified into almost uniform grains
of toner using a classifier almost the same one of the fifteenth
embodiment. The classified toner is attached to an electrostatic
latent image formed on the photosensitive drum 131, which is the
latent image carrier, to develop the image.
The developer of this embodiment is provided with the belt 153
stretched across the rollers 151, 152, which is arranged in
opposite to the photosensitive drum 131. The grains of toner having
required characteristics are transported and attached to the
electric wires 92 of the electric wire line member 91 opposite to
the transfer board 1, then are transferred to the belt 153. A bias
voltage VD from a bias power source 157 for retaining the
transported toner is applied to the belt 153. A bias voltage VD
from a bias power source 158, which is higher than the bias voltage
VD for retaining the toner, is also applied across the
photosensitive drum 131 and the belt 153.
The grains of toner having the required quantity of charge and mass
among the toner transferred and hopped on the transfer board 1 are
attracted to the electric field from the electrode wires 92 of the
electric wire line member 91 opposite to the transfer board 1, and
are transported and attached to the electric wire line member 91.
The attached grains of toner are transported onto the belt 153 by
the traveling wave fields from the electrode wires 92, then sent to
the side where the belt 153 faces the photosensitive drum 131 via
the circulation of the belt 153, and are transported and attached
to the latent image part on the photosensitive drum 131 by a bias
field formed across the belt 153 and the photosensitive drum 131
and an electric field from an electrostatic latent image, thus the
image is developed.
With the constitution described above, it is possible for the
developer of this embodiment to classify charged grains of toner
having a large q/m, and transport and attach them to the belt 153,
then supply them to the developing part. As a result, the
uniformity of the toner for development is enhanced, so that the
quality of development is improved, thus the quality of images is
improved. Besides, the grains of toner having small q/m are not
captured or classified and are discharged from the transfer board
1, then sent back again to the charging brush 143 and the like
through the recovery member 7 and are recharged. Thus, it is
possible to make grains of toner having a large q/m captured and
used for development in a stable manner.
Next, the first embodiment of the image forming apparatus of this
invention comprising the developer of this invention including the
classifier of this invention is described referring to FIG. 47. In
this image forming apparatus, the photosensitive drum 301, i.e.,
latent image carrier, comprises a basic substance 302 on which a
photosensitive layer 303 formed, and is rotated in the arrow
direction shown in FIG. 47. The photosensitive drum 301 is charged
uniformly with a charging apparatus 305, and an electrostatic
latent image is formed on the photosensitive drum 301 when a laser
beam writes in an image read from an exposure part 306 on the
surface of the photosensitive drum 301.
Then, toner is attached to the electrostatic latent image on the
photosensitive drum 301 by the developer 316 of this invention, so
that the electrostatic latent image is visualized. The visualized
latent image is transferred to a transfer paper (recording medium)
319 fed from a paper feed cassette 317 by a transfer roller 302, to
which the voltage from a transfer power source 321 is applied. The
transfer paper 319 with the transferred visualized image is removed
from the surface of the photosensitive drum 301, and is made to
pass through rollers constituting a fixing unit, where the
visualized image is fixed, then is ejected to a ejected paper try
provided on the outside of the image forming apparatus.
Meanwhile, part of the toner remaining on the surface of the
photosensitive drum 301 after the image transfer has been completed
is removed by a cleaning apparatus 326, and residual charge on the
surface of the photosensitive drum 301 is neutralized by a charge
neutralizing lump 326.
The developer 316 houses a pair of charging brushes 331a, 331b
arranged in contact with each other and made to rotate, which is
one example of members for charging toner. The toner T fed from a
toner tank 332 to the charging brushes 331a, 331b is electrified
with friction charge caused by the charging brushes.
The electrified toner is sent to a transfer board 341 constituting
the developer 316, where the transfer board 341 also functions as
part of classifier by transferring the toner for classification.
The developer 316 also comprises an opposite transfer board 342
having an opposite part 342a, which is an opposite member opposed
to transfer board 341 and to which grains of toner having a
required large q/m separated from the toner transferred and hopped
on the transfer board 341 is transported and attached, and a
developing part 342b for transferring the grains of toner attached
to the opposite part 342a and further hopping and transporting them
near the latent image carrier 301, wherein the opposite part 342a
and the developing part 342b are integrally formed. The classifier
further includes a recovery transfer board 343 for transferring
unused grains of toner falling from the end of the transfer board
341 and the opposite transfer board 342 toward a recharging member
(charging brush 331b).
The constitution of the transfer board 341 is the same as that of
the transfer board 1 described before in the embodiments of the
classifiers. Respective constitutions of transfer board 342 and the
recovery transfer board 343 are virtually the same as that of the
transfer board 341, (except that transfer board 342 consists of a
flexible board and is shaped into a reversed transfer course).
Though the drawings of a bias power source and a drive circuit
supplying drive waveforms for the transfer and hopping of toner are
omitted here, they are the same one used in the classifier and
developers described before.
With the constitution described above, it is possible to classify
charged grains of toner having a large q/m, and transport and hop
near the photosensitive drum 301. As a result, the uniformity of
the toner for development is enhanced, so that the quality of
development is improved, thus the quality of images is improved. It
will be appreciated that the classifier and the developer shown in
FIG. 47 do not limit the scope of this embodiment. The classifiers
and the developers described before in respective embodiments are
also applicable to this embodiment.
Next, the second embodiment of the image forming apparatus of this
invention is described referring to FIG. 48, which is the schematic
block diagram of the developer of this embodiment. In this image
forming apparatus, a photosensitive drum 401 (for example, organic
photosensitive body: OPC (Organic Photosensitive Column)) is
rotated clockwise as shown in FIG. 48. When an image manuscript is
placed on a contact glass 402 and a print start switch (not shown
in the figure) is pressed, a scanning optical system 405,
comprising a manuscript lighting source 403 and a mirror 404, and a
scanning optical system 408, comprising a mirrors 406, 407, are
actuated to read the image manuscript.
The scanned image manuscript is read in by a image reading element
410 arranged on the rear of a lens 409 as an image signal, which is
digitized in an image process. The processed signal actuates a
laser diode (LD), which emits a laser beam in response to the
processed signal. The beam is then reflected at a polygon mirror
413 and further reflected at mirror 414 to reach the photosensitive
drum 401, which is charged uniformly with a charging apparatus 415.
The laser beam writes in an electrostatic image on the surface of
the photosensitive drum 401.
Then, toner is attached to the electrostatic image on the surface
of the photosensitive drum 401 by the developer 416 of this
invention, where the image is visualized. The visualized image
(toner image) is transferred to a transfer paper (recording medium)
419 fed from paper feed 417A or 417B via paper feed roller 418A or
418B, as a transfer charger 420 discharges corona currents. The
transfer paper 419 having the transferred image thereon is removed
from the surface of the photosensitive drum 401 and is transferred
on a transfer belt 422 to a fixing roller pair 423. When the
transfer paper 419 passes through the pressure contact part of the
fixing roller pair 423, the visualized image is fixed on the
transfer paper 419, which is further transferred to be ejected to
an ejected paper try 424 provided on the outside of the image
forming apparatus.
Meanwhile, part of the toner remaining on the surface of the
photosensitive drum 401 after the image transfer has been completed
is removed by a cleaning apparatus 425, and residual charge on the
surface of the photosensitive drum 401 is neutralized by a charge
neutralizing lump 426.
As shown in FIG. 49, the developer 416 comprises a toner hopper 431
for storing the toner, an agitator 432 for agitating the toner in
the toner hopper 431, a charging roller 434 for charging the toner
in the toner hopper 431 and supplying the toner to a toner box 433,
and a doctor blade 435 arranged in contact with the periphery of
the charging roller 434.
The toner supplied to the toner box 433 is sent to a transfer board
441 for transferring the toner for classification, which is also
included in the developer 416. The developer 416 further comprises
an opposite transfer board 442 having an opposite part 442a, which
is an opposite member opposed to transfer board 441 and to which
grains of toner having a required large q/m separated from the
toner transferred and hopped on the transfer board 441 is
transported and attached, and a developing part 442b for
transferring the grains of toner attached to the opposite part 442a
and further transporting and hopping them near the photosensitive
drum 401, wherein the opposite part 442a and the developing part
442b are integrally formed. The developer 416 further includes a
recovery transfer board 443 for transferring unused grains of toner
falling from the end of the transfer board 441 and the opposite
transfer board 442 toward a recharging member (charging roller
434).
As described in the first embodiment of the image forming
apparatus, the constitution of transfer board 441 is the same as
that of the transfer board 1 described before in the embodiments of
the classifiers. Respective constitutions of transfer board 442 and
the recovery transfer board 443 are virtually the same as that of
the transfer board 441, (except that transfer board 442 consists of
a flexible board and is shaped into a reversed transfer course).
Though the drawings of a bias power source and a drive circuit
supplying drive waveforms for the transfer and hopping of toner are
omitted here, they are the same one used in the classifier and
developers described before.
With this arrangement, the grains of toner having a large q/m are
classified out of supplied charged toner, and are transported and
attached to the opposite transfer board 442, then further
transferred to the vicinity of the photosensitive drum 401, where
the classified toner T hop. To attach the toner hopping near the
photosensitive drum 401 to the latent image on the photosensitive
drum 401, preset electric fields are required to be generated. It
is required to set in such a way that the combined electric field
between electric fields generated by the average of the pulse drive
voltage applied to the electrodes of the opposite transfer board
442 and that generated by the voltage of latent image formed on the
photosensitive drum 401 attracts the toner to the photosensitive
drum 401. It is also required to set in such a way that the
combined electric field between the electric fields generated by
the average of the pulse drive voltage applied to the electrodes of
the opposite transfer board 442 and that generated by the voltage
of the part of the photosensitive drum 401 where latent image is
not formed repels the toner against the photosensitive drum 401. It
is also desirable that drive waveforms for transferring classified
toner and that for transferring and hopping the toner near the
latent image carrier be different.
Hopping grains of toner are already free from an absorption force
capturing them on the opposite transfer board 442, and can be
easily transported to the latent image carrier (photosensitive drum
401), so that a development providing a high quality image can be
carried out at a relatively low voltage.
In a conventional jumping development method, an applying voltage
generating electric field stronger enough to overcome an adhesive
force of toner to a developing roller must be provided for removing
charged toner from the developing roller to transport to a
photosensitive body, which means that a bias DC voltage of more
than 600 to 900 V is required. On the other hand, according to the
ETH phenomenon method, while the adhesive force of a grain of toner
is usually 50 to 200 nN, the adhesive force becomes almost zero
because the grains of toner are hopping on the opposite transfer
board 442. Therefore, the force required to removing the toner from
the opposite transfer board 442 is not required, so that the toner
can be transported sufficiently to the photosensitive body at a low
voltage.
The width L of electrodes and the space R between electrodes of the
opposite transfer board 442 are set within the range conforming to
that of the transfer board 1 of the classifier described before.
This electrode arrangement allows the electrodes to generate
electric line of force as a vertical component, which makes grains
of toner hop on the electrodes 12. Therefore, it becomes possible
to hop the toner more effectively, thus improving a developing
efficiency.
The thickness of the surface protective layer 13 of the opposite
transfer board 442, at least that of the part near the latent image
carrier where the hopping occurs, is also set within the range
conforming to that of the transfer board 1 of the classifier
described before. At the height equal to the diameter of a grain of
toner from the center surface of electrode 12, the vertical
strength of electric field capable of giving a force to hop the
toner is more than (5E+5) V/m. As the strength eliminating a
problem of absorption, more than (1 E+6) V/m is desirable. Further,
as a more desirable strength to give an enough force, more than
(2E+6) V/m is desirable.
The thickness of the surface protective layer affects the strength
of electric field acting on the grains of toner hopping near the
center surface of the electrode. Making the surface protective
layer thicker increases electric fields heading for the adjacent
electrode through the protective layer having a dielectric constant
higher than that of air. As a result, the vertical component of the
field is reduced. Therefore, an allowable range of the thickness of
the surface protective layer to the hopping efficiency decrease is
10 .mu.m or less, and a range for eliminating a concern of electric
field attenuation in the vertical direction is 5 .mu.m or less.
With a surface protective layer of that range, it is possible to
obtain a desirable electric field of more than (1 E+6) V/m, which
gives an enough force to hop the toner free from the problem of
absorption.
As for the charge potential of the surface of photosensitive drum
401, i.e., the latent image carrier, if toner is negatively
charged, it is set to -300 V or less, and if positively charged, it
is set to +300 V or less. Therefore, the charge potential of the
surface of the latent image carrier should be 300V or less.
With the above setting, when fine-pitched electrodes are formed, a
quite a large electric fields are generated even if a voltage
applied between the electrodes 12 is a low voltage of 100 to 150 V
or less, thus toner sticking to the surface of electrodes 12 is
easily removed and hopped. Besides, the above arrangement reduces
or eliminates ozone or NOx produced upon electrifying the
photosensitive body, such as OPC, making the image forming
apparatus advantageous for an environment problem and the
photosensitive body more durable.
Therefore, in this embodiment, it is not necessary to apply a high
bias voltage of 500 V to several KV across the developing roller
and the photosensitive body, as in the case of conventional method,
to remove the toner sticking to the developing roller surface or
carrier surface. Thus it is possible to form a latent image and
develop it while setting the charge potential of photosensitive
body to a very low value.
For example, when an OPC photosensitive body with a surface CTL
(Charge Transport Layer) of 15 .mu.m thick and a dielectric
constant .epsilon. of 3 is used for charged toner having charge
density of -3 E-4 C/m.sup.2, the surface potential of the
photosensitive body is -170 V. In this case, the surface potential
becomes -50 V in average when a pulse drive voltage of 0 to -100 V
with a duty of 50% is applied as an applied voltage for the
electrodes of the transfer board. When toner is negatively charged
and the above setting and result is obtained, the electric fields
formed between the electrodes of transfer board and the OPC
photosensitive body comes to such a state described before that
respective fields for attracting or repulsing the toner are set to
a prescribed strength.
When the above state of electric fields is achieved, development
becomes possible with a given gap between the transfer board and
the OPC photosensitive body of 0.2 to 0.3 .mu.m. While this
requirement varies according to Q/M of toner, an applied voltage
for the electrodes of the transfer boards, and a print speed, i.e.,
the rotating speed of the photosensitive body, development can be
carried out in a sufficient manner with a charging potential for
the photosensitive body of -300 V or less when the toner is
negatively charged. If development efficiency is prioritized,
charging potential of -100 V or less is also allowable. If the
toner is positively charged, the charging potential is positive
potential.
The gap between the photosensitive drum 401, i.e., latent image
carrier, and the opposite transfer board 442 is further described.
When the gap between the toner transfer surface and the latent
image carrier is set within a range of 2 to 100 times the height of
the hopping of toner, the grains of toner hopping high further fly
up to the latent image carrier and contribute to a development
process. Contrary to that, the grains of toner hopping low cannot
reach the latent image carrier, thus do not contribute to the
development process.
FIG. 15 shows an example of the relation between an applied voltage
and the height of hopping of the grains of toner. For example, when
the applied voltage is set to 100 V and Q/M of the grains of toner
is changed to -10 .mu.C/g, -20 .mu.C/g, and -30 .mu.C/g, the speed
of the grains of toner in the vertical direction changes to gain
the maximum speed of 0.65 m/sec to 1.25 m/sec. The height of the
hopping increases from 100, to 125 to 150 .mu.m as Q/M of the toner
is increased.
Therefore, when toner having a certain Q/M distribution is
transferred to the area for hopping to the latent image carrier,
the grains of toner having a small Q/M, for example, of smaller
than 10 to 5 .mu.C/g, cannot contribute to development process,
because their jump height is not enough. As a result, only the
grains of toner having a Q/M more than a prescribed value are used
for development.
Using the toner having a Q/M more than a prescribed value makes
possible to attach the toner surely to a latent image, and
eliminates a splatter or move of attached toner, thus enables a
development producing high quality images. Further, it also becomes
possible to prevent a foul printing caused by weakly charge toner
or a group of grains of reversely charged toner. Therefore, the
developer of this invention, in which toner is hopped, makes
possible to select the grains of toner having an Q/M effective for
contributing to the development process, thus to obtain an image
forming apparatus having a developing unit (developer) capable of
performing a high quality development at a low voltage.
The gap between the toner transfer surface and the latent image
carrier may be set within a range of 1/2 to 2 times the height of
the hopping of toner.
In this case, most part of hopping grains of toner collide against
the surface of the latent image carrier with a prescribed speed,
irrespective of the electric field from a latent image on the
latent image carrier. As a result, unnecessary grains of toner
attached to the area other than the latent image have a weak
absorption force, and the grains of toner forming the surface of
layer-shaped grains of toner attached to the latent image are also
have weak absorption force. Both grains of toner are eventually
removed as following grains of toner collide against the latent
image carrier, which produces a more great scavenger effect, making
possible to obtain more sharp images. Besides, in this case, more
large volume of toner can be transported to the surface of
photosensitive body, so that more strong images can be developed at
a high speed.
Next, the transfer board, the opposite transfer board, and the
drive frequency of drive waveforms applied to the electrodes 12 of
the recovery transfer board are described referring to FIG. 51,
which shows a result of a measurement of the relation between a
drive frequency and a transfer speed. In the figure, the axis of
ordinate represents transfer speed, but also indicates the hopping
of grains of toner in the vertical direction.
As shown in FIG. 51, the transfer speed goes up as the drive
frequency increases. This is because the number of hopping of the
grains of toner near the electrodes increase as the direction of
electric fields is changed more frequently.
The result indicates that the hopping and transfer of toner are
correctly performed when the drive frequency of drive waveforms is
set within a range of 1 to 15 KH. Therefore, high quality images
can be formed by setting a proper drive frequency of drive
waveforms, according to a print speed or the strength of
images.
When the strength of images is constant, the higher a print speed
is, the more the amount of toner consumed for development is. When
a print speed is constant, the high the strength of images is, the
more the amount of toner consumed for development is. When a
consumed amount of toner increases, more toner needs to be supplied
to the toner hopping part (developing part). By setting a proper
drive frequency of drive waveforms, according to a print speed or
the strength of images, a shortage of toner supply can be prevented
and high quality images can be created.
Next, another example of the transfer board, the opposite transfer
board, and the drive frequency of drive waveforms applied to the
electrodes 12 of the recovery transfer board are described
referring to FIG. 52. The figure shows an example that drive
waveforms of n phases (three phases in the figure) are applied in
such a way that the polarity of one phase is different from that of
other two phases. When the polarities of three phases are different
to each other, (positive to negative to zero potential), the
potential difference between adjacent electrodes becomes high, so
that the hopping can be carried out without fail.
Next, the powder charging and selecting apparatus is described as
another application of the classifier of this invention, referring
to FIGS. 53 and 54. FIG. 53 is the flat view showing a powder
charging and selecting apparatus, and FIG. 54 is the modeled
sectional view of the powder charging and selecting apparatus.
An airflow generating apparatus 501 generates a jet airflow 501a,
of which the relative humidity is lowered to keep the atmosphere of
jet airflow lower than 70% by a nozzle jet method using an air
pump, a jet method utilizing high-pressure adiabatic expansion, a
turbofan method and the like. A powder supply 503 is arranged on
the side of a transfer passage 502 through which a jet airflow 501a
flows. The powder supply 503 supplies powder 505 by means of a
supply roller 504 to the transfer passage 502, then the powder 505
is transfer through the transfer passage 502 by the jet airflow
501a to a cyclone apparatus 510. The powder 505 transferred by a
gas-phase transfer is charged by the friction with a charging
mechanism provided on the pipe wall 502a of the transfer passage
502, and is further charged by the friction with the charging
mechanism on the lid inner wall on the upper part of the cyclone
apparatus 510.
More specifically, the pipe wall 502a of the transfer passage 502
and the lid inner wall on the upper part of the cyclone apparatus
510 are made of a charging function material, and the powder
carried by the airflow made to come in contact with the charging
function material to come to have a friction charge.
The charging function material comes to have a charge polarity
reverse to that of the powder upon contacting the powder, such as
toner, facilitating a proper friction charge of the powder. The
strength of charge can be adjusted by selecting a proper material.
More specifically, the charging function material can be selected
from a substance of acrylic series, silicon series, fluorine resin
series, urea resin series, polyester series, polyimide series,
polyamide series, polyformamide series, poly vinyl chloride series,
olefin series, anine series, polyurethane series, and ethyl
cellulose series, or a mixture of these substance. The charging
function material can also selected among metal oxide conductors,
compound semiconductors, or mixtures consisting of these conductors
or semiconductors and the above resin series substances.
The cyclone apparatus 510 classifies or selects the charge powder
by double-clone or multi-clone method, and comprises a
reversed-cone-shape cylindrical body 511, an upper lid 512, and a
powder recovery part 513 arranged below the cylindrical body 511,
where one end of a electric wire line member 515 constituted as
described before faces the inside of the cylindrical body 511. Each
electric wire 516 of the electric wire line member 515 is sheathed
with an insulating protective film and the electric wire line
member 515 penetrates through a duct 517 to face the other end of
it in a toner storing part 518. A drive circuit, which is not shown
in the figure, applies n-phase drive waveforms for generating
electric fields for transferring the powder by an electric
statistic force to each electric wire 516 of the electric wire line
member 515.
The powder recovered at the powder recovery part 513 of the cyclone
apparatus 510 is supplied again to the powder supply 503 via a
re-comminuting part 520.
Among the powder moving through the cyclone apparatus 510 by being
carried by the airflow, the grains of powder that are properly
charged have a good dispersibility owing to a charge repulsion
between each grain of powder and have a great flowability to avoid
granulation. As a result, such grains of powder receives traveling
wave fields generated by each electric wire 516 of the electric
wire line member 515 and are sent along the electric wire line
member 515, even in the vortex caused by the cyclone apparatus 510,
to the toner storing part 518 and stored there.
Meanwhile, the grains of powder having a small charge and inferior
dispersibility tend to granulate to form lumps or clusters and have
a relatively large mass. As a result, such grains of powder are not
retained by traveling wave fields generated by each electric wire
516 of the electric wire line member 515 and falls into the
recovery part 513 arranged below.
As described above, the charging and selection of toner during a
manufacturing process of toner is facilitated by using the powder
charging and selecting apparatus.
According to the description made heretofore, the classifier of the
present invention comprises the transfer member having a plurality
of electrodes for generating electric fields for transporting
powder while transferring and hopping the powder by an
electrostatic force, and the opposite member to which the powder
transferred by the transfer member is transported and attached, the
opposite member being almost opposite to the transfer member.
Therefore, the classifier of the present invention makes possible
to classify the powder with a high accuracy and a simple
constitution.
According to the classifier of the present invention, powder is
transported while it is transferred and hopped on the transfer
board by an electrostatic force, and the powder transferred and
hopped is classified by transporting and attaching the powder to
another member by an electric field. Therefore, the classifier of
the present invention makes possible to classify the powder with a
high accuracy and a simple constitution.
According to the developer of the present invention, the powder
classified by the classifier of this invention is supplied to the
developing means, so that the quality of development is
improved.
According to the image forming apparatus of the present invention,
the image forming apparatus is provided with the classifier of this
invention or the developer of the present invention, so that images
are formed using uniformed powder, thus the quality of development
is improved.
While the present invention has been described with a preferred
embodiment, this description is not intended to limit our
invention. Various modifications of the embodiment will be apparent
to those skilled in the art. It is therefore contemplated that the
appended claims will cover any such modifications or embodiments as
fall within the true scope of the invention.
* * * * *